open-gpu-kernel-modules/kernel-open/nvidia-uvm/uvm_va_block.h

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#ifndef __UVM_VA_BLOCK_H__
#define __UVM_VA_BLOCK_H__

#include "uvm_forward_decl.h"
#include "uvm_types.h"
#include "uvm_linux.h"
#include "nv-kref.h"
#include "uvm_common.h"
#include "uvm_perf_module.h"
#include "uvm_processors.h"
#include "uvm_lock.h"
#include "uvm_test_ioctl.h"
#include "uvm_tracker.h"
#include "uvm_pmm_gpu.h"
#include "uvm_perf_thrashing.h"
#include "uvm_perf_utils.h"
#include "uvm_va_block_types.h"
#include "uvm_range_tree.h"
#include "uvm_mmu.h"
#include "nv-kthread-q.h"

#include <linux/mmu_notifier.h>
#include <linux/wait.h>

// VA blocks are the leaf nodes in the uvm_va_space tree for managed allocations
// (VA ranges with type == UVM_VA_RANGE_TYPE_MANAGED):
//
//  UVM: uvm_va_space -> uvm_va_range -> uvm_va_block
//  HMM: uvm_va_space -> uvm_va_block
//
// Each VA block is contained within a single VA range, and contains state on
// VAs covered by that block. Most importantly, the block tracks the current
// state of the virtual-to-physical mappings for all VAs within that block
// across all processors, along with the physical residency location for each
// VA.
//
// The block serializes both CPU and GPU operations on all VAs under that block.
// The CPU work is serialized with the block lock, and the GPU work is
// serialized by the block work tracker which itself is protected by the block
// lock.
//
// The size of each block varies from the size of the smallest VA range
// (PAGE_SIZE) to the max block size specified by UVM_VA_BLOCK_BITS. No block
// will span a 2^UVM_VA_BLOCK_BITS boundary in VA space. The size of the block
// is determined by the alignment of the parent VA range and the block's
// placement within the range.
//
// Note that this means user space will get best allocation efficiency if it
// allocates memory in 2^UVM_VA_BLOCK_BITS naturally-aligned chunks.

// enums used for indexing into the array of pte_bits bitmaps in the VA block
// which hold the current state of each PTE. For a given {processor, PTE}, the
// bits represented here must be enough to re-create the non-address portion of
// the PTE for that processor.

// If _READ is not set, the PTE mapping is not valid.
// If _WRITE is set, _READ is also set (_WRITE implies _READ).
typedef enum
{
    UVM_PTE_BITS_CPU_READ,
    UVM_PTE_BITS_CPU_WRITE,
    UVM_PTE_BITS_CPU_MAX
} uvm_pte_bits_cpu_t;

// If _READ is not set, the PTE mapping is not valid.
// If _WRITE is set, _READ is also set (_WRITE implies _READ).
// If _ATOMIC is set, _WRITE is also set (_ATOMIC implies _WRITE and _READ).
//
// TODO: Bug 1764925: Track volatile here too if we add GPU L2 caching
typedef enum
{
    UVM_PTE_BITS_GPU_READ,
    UVM_PTE_BITS_GPU_WRITE,
    UVM_PTE_BITS_GPU_ATOMIC,
    UVM_PTE_BITS_GPU_MAX
} uvm_pte_bits_gpu_t;

typedef struct
{
    // Per-page residency bit vector, used for fast traversal
    // of resident pages.
    //
    // This follows the same semantics as the CPU residency bit vector and
    // notably each bit still represents a PAGE_SIZE amount of data, but the
    // physical GPU memory is tracked by an array of GPU chunks below.
    uvm_page_mask_t resident;

    // Pages that have been evicted to sysmem
    uvm_page_mask_t evicted;

    NvU64 *cpu_chunks_dma_addrs;

    // Array of naturally-aligned chunks. Each chunk has the largest possible
    // size which can fit within the block, so they are not uniform size.
    //
    // The number of chunks in the array is calculated using
    // block_num_gpu_chunks. The size of each chunk is calculated using
    // block_gpu_chunk_index.
    uvm_gpu_chunk_t **chunks;

    // These page table ranges are not necessarily all used at the same time.
    // The block might also be too small or not aligned properly to use the
    // larger ranges, in which case they're never allocated.
    //
    // Once a range is allocated we keep it around to avoid constant allocation
    // overhead when doing PTE splitting and merging.
    //
    // Check range.table to see if a given range has been allocated yet.
    //
    // page_table_range_big's range covers the big PTEs which fit within the
    // interior of this block. See the big_ptes field.
    uvm_page_table_range_t page_table_range_2m;
    uvm_page_table_range_t page_table_range_big;
    uvm_page_table_range_t page_table_range_4k;

    // These flags are ignored unless the {block, gpu} pair supports a 2M page
    // size. In that case it's the responsibility of the block code to make the
    // lower page tables active by calling uvm_page_tree_write_pde.
    //
    // They can be allocated and activated separately, so we have to track them
    // separately.
    //
    // Activated only means that uvm_page_tree_write_pde has been called at some
    // point in the past with the appropriate range allocated. It does not imply
    // that the 2M entry is a PDE (see pte_is_2m).
    bool activated_big;
    bool activated_4k;

    // For {block, gpu} pairs which support the 2M page size, the page table
    // ranges are uninitialized on allocation. This flag tracks whether the big
    // PTEs have been initialized.
    //
    // We don't need an equivalent flag for the 4k range because we always write
    // just the 4k PTEs not covered by higher-level PTEs. Big PTEs however can
    // be allocated and activated late while the 4k PTEs are already active, in
    // which case we need to initialize the entire big range.
    bool initialized_big;

    // Sticky state to split PTEs to 4k and keep them there. Used when a fatal
    // fault has been detected on this GPU to avoid false dependencies within
    // the uTLB for fatal and non-fatal faults on the same larger PTE, which
    // could lead to wrong fault attribution.
    bool force_4k_ptes;

    // This table shows the HW PTE states given all permutations of pte_is_2m,
    // big_ptes, and pte_bits. Note that the first row assumes that the 4k page
    // tables have been allocated (if not, then no PDEs are allocated either).
    //
    // |-------------- SW state --------------|------------------- HW state --------------------|
    //  pte_is_2m  pte_is_big  pte_bits[READ] | Page size  PDE0(2M only)  Big PTE       4k PTE
    //  ----------------------------------------------------------------------------------------
    //  0          0           0              | 4k         Valid PDE      Invalid [1]   Invalid
    //  0          0           1              | 4k         Valid PDE      Invalid [1]   Valid
    //  0          1           0              | Big        Valid PDE      Unmapped [2]  x
    //  0          1           1              | Big        Valid PDE      Valid         x
    //  1          must be 0   0              | 2M         Invalid        x             x
    //  1          must be 0   1              | 2M         Valid PTE      x             x
    //
    // [1]: The big PTE may be unallocated, in which case its pointer won't be
    //      valid in the parent PDE. If the big PTE is allocated, it will be
    //      invalid so the 4k PTEs are active.
    //
    // [2]: The unmapped big PTE pattern differs from the invalid pattern, and
    //      it prevents HW from reading the 4k entries. See the unmapped_pte()
    //      MMU HAL function.

    // If pte_is_2m is true, there is a 2M PTE covering this VA block (valid or
    // invalid). If false then we're in one of the following scenarios:
    // 1) This {block, gpu} does not support 2M pages.
    // 2) 2M pages are supported but the page_table_range_2m has not been
    //    allocated (implying that the other page table ranges have not been
    //    allocated either).
    // 3) page_table_range_2m has been allocated, but the big_ptes bitmap should
    //    be used to determine the mix of big and 4k PTEs.
    bool pte_is_2m;

    // When pte_is_2m is false, this block consists of any possible mix of big
    // and 4k PTEs. This bitmap describes that mix. A set bit indicates that the
    // corresponding big-page-sized region of the block is covered by a big PTE.
    // A cleared bit indicates that it is covered by 4k PTEs.
    //
    // Neither setting implies that the PTE currently has a valid mapping, it
    // just indicates which PTE is read by the GPU (see the table above).
    //
    // The indices represent the corresponding big PTEs in the block's interior.
    // For example, a block with alignment and size of one 4k page on either
    // side of a big page will only use bit 0. Use uvm_va_block_big_page_index to look
    // the big_ptes index of a page.
    //
    // The block might not be able to fit any big PTEs, in which case this
    // bitmap is always zero. Use uvm_va_block_gpu_num_big_pages to find the number of
    // valid bits in this mask.
    DECLARE_BITMAP(big_ptes, MAX_BIG_PAGES_PER_UVM_VA_BLOCK);

    // See the comments for uvm_va_block_mmap_t::cpu.pte_bits.
    //
    // The major difference is that these bits are always accurate since, unlike
    // the CPU PTEs, the UVM driver is in full control of these mappings.
    //
    // Note that the granularity is always PAGE_SIZE, not whatever GPU PTE size
    // happens to currently map these regions. PAGE_SIZE is the minimum
    // granularity of operations on the VA blocks. As a future optimization we
    // could consider sub-PAGE_SIZE operations if PAGE_SIZE > 4K and the CPU
    // isn't involved, for example false sharing among peer GPUs.
    uvm_page_mask_t pte_bits[UVM_PTE_BITS_GPU_MAX];

} uvm_va_block_gpu_state_t;

// TODO: Bug 1766180: Worst-case we could have one of these per system page.
//       Options:
//       1) Rely on the OOM killer to prevent the user from trying to do that
//       2) Be much more space-conscious in this struct (difficult)
//       3) Cap the per-process range and/or block count, like vm.max_map_count
//          does for vmas
struct uvm_va_block_struct
{
    // Reference count for this block. References are held by:
    // - The parent VA range for managed blocks or VA space for HMM blocks
    // - The reverse map
    // - The eviction path temporarily when attempting to evict a GPU page under
    //   this block
    //
    // This isn't protected by the lock on the eviction path, so it must be
    // atomic. nv_kref provides that.
    nv_kref_t kref;

    // Lock protecting the block. See the comment at the top of uvm.c.
    uvm_mutex_t lock;

    // Parent VA range. Managed blocks have this set. HMM blocks will have
    // va_range set to NULL and hmm.va_space set instead. Dead blocks that are
    // waiting for the last ref count to be removed have va_range and
    // hmm.va_space set to NULL (could be either type of block).
    //
    // This field can be read while holding either the block lock or just the VA
    // space lock in read mode, since it can only change when the VA space lock
    // is held in write mode.
    uvm_va_range_t *va_range;

    // Virtual address [start, end] covered by this block. These fields can be
    // read while holding either the block lock or just the VA space lock in
    // read mode, since they can only change when the VA space lock is held in
    // write mode.
    NvU64 start;
    NvU64 end;

    // Per-processor residency bit vector, used for fast lookup of which
    // processors are active in this block.
    //
    // A set bit means the corresponding processor has a coherent physical copy
    // of memory somewhere in the block. The per-processor state must then be
    // inspected to find out which pages. The processor may or may not have a
    // mapping to that physical memory, however.
    //
    // A cleared bit means the corresponding processor does not have a coherent
    // physical copy of any pages under this block. The processor may still have
    // cached pages allocated for future use, however. It also may have mappings
    // to pages resident on other processors.
    uvm_processor_mask_t resident;

    // Per-processor mapping bit vector, used for fast lookup of which
    // processors are active in this block.
    //
    // A set bit means the corresponding processor has an active, valid page
    // table mapping to some VA in this block. The per-processor pte_bits state
    // must then be inspected to find out the mapping address and permissions.
    //
    // A cleared bit means the corresponding processor has no virtual mappings
    // within this block (all pte_bits entries are 0).
    uvm_processor_mask_t mapped;

    // Per-processor evicted bit vector, used for fast lookup of which GPUs
    // have evicted pages in this block.
    //
    // A set bit means the corresponding processor was the residency of some of
    // the pages in the block when they were evicted due to memory capacity
    // limitations. The per-processor state must then be inspected to find out
    // which pages.
    //
    // A cleared bit means the corresponding processor has no evicted pages
    // within this block (all evicted entries are 0).
    uvm_processor_mask_t evicted_gpus;

    struct
    {
        // Per-page residency bit vector, used for fast traversal of resident
        // pages.
        //
        // A set bit means the CPU has a coherent copy of the physical page
        // resident in its memory, and that the corresponding entry in the pages
        // array is present. This does not mean that the coherent copy is
        // currently mapped anywhere, however. A page may be resident on
        // multiple processors when in read-duplicate mode.
        //
        // A cleared bit means the CPU does not have a coherent copy of that
        // page resident. The corresponding entry in the pages array may or may
        // not present. If the entry is present, it's a cached page which can be
        // reused in the future.
        //
        // Allocating PAGES_PER_UVM_VA_BLOCK is overkill when the block is
        // smaller than UVM_VA_BLOCK_SIZE, but it's not much extra memory
        // overhead on the whole.
        uvm_page_mask_t resident;

        // CPU memory chunks represent physically contiguous CPU memory
        // allocations. See uvm_pmm_sysmem.h for more details on CPU chunks.
        // This member is meant to hold an opaque value indicating the CPU
        // chunk storage method. For more details on CPU chunk storage,
        // see uvm_cpu_chunk_storage_type_t in uvm_va_block.c.
        unsigned long chunks;

        // Per-page allocation bit vector.
        //
        // A set bit means that a CPU page has been allocated for the
        // corresponding page index.
        uvm_page_mask_t allocated;

        // Per-page mapping bit vectors, one per bit we need to track. These are
        // used for fast traversal of valid mappings in the block. These contain
        // all non-address bits needed to establish a virtual mapping on this
        // processor (permissions, cacheability, etc).
        //
        // A cleared bit in UVM_PTE_BITS_CPU_READ means the CPU has no valid
        // virtual mapping to that address (the access will fault). Further,
        // UVM_PTE_BITS_CPU_WRITE is guaranteed to also be clear.
        //
        // A set bit in UVM_PTE_BITS_CPU_READ means the CPU has a valid mapping
        // at that address with at least read permissions. The physical page for
        // that mapping is contained in the pages array. If
        // UVM_PTE_BITS_CPU_WRITE is not set, the mapping is read-only.
        // Otherwise, the mapping is read-write.
        //
        // For managed allocations, this is the maximum permissions a PTE
        // could have, but not necessarily the actual current permissions of the
        // CPU PTEs. The UVM driver will never change the PTEs without updating
        // this state, but the kernel can downgrade our CPU mappings at any time
        // without notifying the UVM driver (for example in response to user
        // space calling madvise with MADV_DONTNEED).
        //
        // For HMM allocations, this is the minimum permission the CPU has since
        // Linux can upgrade a read-only PTE to read-write without notifying
        // the UVM driver. This is why read duplication isn't currently
        // supported.
        // TODO: Bug 3660922: Need to handle read duplication at some point.
        uvm_page_mask_t pte_bits[UVM_PTE_BITS_CPU_MAX];

        // Whether the CPU has ever mapped a page on this VA block. This is
        // used to force GMMU PDE1 pre-population on ATS systems. See
        // pre_populate_gpu_pde1 in uvm_va_block.c for more information.
        NvU8 ever_mapped        : 1;

        // We can get "unexpected" faults if multiple CPU threads fault on the
        // same address simultaneously and race to create the mapping. Since
        // our CPU fault handler always unmaps to handle the case where the
        // kernel downgrades our CPU mappings, we can introduce an infinite
        // stream of CPU faults in multi-threaded workloads.
        //
        // In order to handle this scenario, we keep track of the first thread
        // that faulted on a page with valid permissions and the timestamp.
        // Then, we keep track of the subsequent faults on that page during a
        // window of time. If the first thread faults again on the page, that
        // will indicate that the mapping has been downgraded by the kernel and
        // we need to remap it. Faults from the rest of threads are just
        // ignored. The information is also cleared on the following events:
        // - The tracking window finishes
        // - The page is unmapped
        struct
        {
            // Timestamp when the first fault was detected. This also is used
            // as a flag that the contents of this struct are valid
            NvU64             first_fault_stamp;

            // First thread that faulted while having valid permissions. we
            // don't take a reference on the pid so we shouldn't ever use it
            // for task-lookup in the kernel. We only use it as a heuristic so
            // it's OK if the pid gets destroyed or reused.
            pid_t             first_pid;

            // Index of the page whose faults are being tracked
            uvm_page_index_t  page_index;
        } fault_authorized;
    } cpu;

    // Per-GPU residency and mapping state
    //
    // TODO: Bug 1766180: Even though these are pointers, making this a static
    //       array will use up a non-trivial amount of storage for small blocks.
    //       In most cases we won't have anywhere near this many GPUs active
    //       anyway. Consider using a dense array of just the GPUs registered in
    //       this VA space, depending on the perf of accessing that array and on
    //       how noticeable this memory overhead actually is.
    uvm_va_block_gpu_state_t *gpus[UVM_ID_MAX_GPUS];

    // Mask to keep track of the pages that are read-duplicate
    uvm_page_mask_t read_duplicated_pages;

    // Mask to keep track of the pages that are not mapped on any non-UVM-Lite
    // processor.
    //     0: Page is definitely not mapped by any processors
    //     1: Page may or may not be mapped by a processor
    //
    // This mask sets the bit when the page is mapped on any non-UVM-Lite
    // processor but it is not always unset on unmap (to avoid a performance
    // impact). Therefore, it can contain false negatives. It should be only
    // used for opportunistic optimizations that have a fast path for pages
    // that are not mapped anywhere (see uvm_va_block_migrate_locked, for
    // example), but not the other way around.
    uvm_page_mask_t maybe_mapped_pages;

    // Tracks all outstanding GPU work related to this block: GPU copies, PTE
    // updates, TLB invalidates, etc. The residency and mapping state is only
    // valid once this tracker is done.
    //
    // CPU operations need to wait for this tracker to be done. GPU operations
    // need to acquire it before pushing their work, then that work must be
    // added to this tracker before the block's lock is dropped.
    uvm_tracker_t tracker;

    // A queue item for establishing eviction mappings in a deferred way
    nv_kthread_q_item_t eviction_mappings_q_item;

    uvm_perf_module_data_desc_t perf_modules_data[UVM_PERF_MODULE_TYPE_COUNT];

    // Prefetch infomation that is updated while holding the va_block lock but
    // records state while the lock is not held.
    struct
    {
        uvm_processor_id_t last_migration_proc_id;

        NvU16 fault_migrations_to_last_proc;
    } prefetch_info;

#if UVM_IS_CONFIG_HMM()
    struct
    {
        // The MMU notifier is registered per va_block.
        struct mmu_interval_notifier notifier;

        // This is used to serialize migrations between CPU and GPU while
        // allowing the va_block lock to be dropped.
        // This must be acquired before locking the va_block lock if the
        // critical section can change the residency state.
        // Do not access directly, use the uvm_hmm_migrate_*() routines.
        uvm_mutex_t migrate_lock;

        // Sequence number to tell if any changes were made to the va_block
        // while not holding the block lock and calling hmm_range_fault().
        unsigned long changed;

        // Parent VA space pointer. It is NULL for managed blocks or if
        // the HMM block is dead. This field can be read while holding the
        // block lock and is only modified while holding the va_space write
        // lock and va_block lock (same as the va_range pointer).
        uvm_va_space_t *va_space;

        // Tree of uvm_va_policy_node_t. The policy node ranges always cover
        // all or part of a VMA range or a contiguous range of VMAs within the
        // va_block. Policy nodes are resized or deleted when the underlying
        // VMA range is changed by Linux via the invalidate() callback.
        // Otherwise, policies could be stale after munmap().
        // Locking: The va_block lock is needed to access or modify the tree.
        uvm_range_tree_t va_policy_tree;

        // Storage node for range tree of va_blocks.
        uvm_range_tree_node_t node;
    } hmm;
#endif
};

// We define additional per-VA Block fields for testing. When
// uvm_enable_builtin_tests is defined, all VA Blocks will have
// uvm_va_block_wrapper_t size. Otherwise, the test fields are not available.
// Use the uvm_va_block_get_test function defined below to obtain a safe
// pointer to uvm_va_block_test_t from a uvm_va_block_t pointer.
struct uvm_va_block_wrapper_struct
{
    uvm_va_block_t block;

    struct uvm_va_block_test_struct
    {
        // Count of how many page table allocations should be forced to retry
        // with eviction enabled. Used for testing only.
        NvU32 page_table_allocation_retry_force_count;

        // Count of how many user pages allocations should be forced to retry
        // with eviction enabled. Used for testing only.
        NvU32 user_pages_allocation_retry_force_count;

        // Mask of chunk sizes to be used for CPU chunk allocations.
        // The actual set of chunk sizes to be used will be the set resulting
        // from AND'ing this value with the value of
        // uvm_cpu_chunk_allocation_sizes module parameter.
        NvU32 cpu_chunk_allocation_size_mask;

        // Subsequent operations that need to allocate CPU pages will fail. As
        // opposed to other error injection settings, this one fails N times
        // and then succeeds instead of failing on the Nth try. A value of ~0u
        // means fail indefinitely.
        // This is because this error is supposed to be fatal and tests verify
        // the state of the VA blocks after the failure. However, some tests
        // use kernels to trigger migrations and a fault replay could trigger
        // a successful migration if this error flag is cleared.
        NvU32 inject_cpu_pages_allocation_error_count;

        // Force the next eviction attempt on this block to fail. Used for
        // testing only.
        bool inject_eviction_error;

        // Force the next successful chunk allocation to then fail. Used for testing
        // only to simulate driver metadata allocation failure.
        bool inject_populate_error;

        // Force the next split on this block to fail.
        // Set by error injection ioctl for testing purposes only.
        bool inject_split_error;
    } test;
};

// Tracking needed for supporting allocation-retry of user GPU memory
struct uvm_va_block_retry_struct
{
    // A tracker used for all allocations from PMM.
    uvm_tracker_t tracker;

    // List of allocated chunks (uvm_gpu_chunk_t). Currently all chunks are of
    // the same size. However it can contain chunks from multiple GPUs. All
    // remaining free chunks are freed when the operation is finished with
    // uvm_va_block_retry_deinit().
    struct list_head free_chunks;

    // List of chunks allocated and used during the block operation. This list
    // can contain chunks from multiple GPUs. All the used chunks are unpinned
    // when the operation is finished with uvm_va_block_retry_deinit().
    struct list_head used_chunks;
};

// Module load/exit
NV_STATUS uvm_va_block_init(void);
void uvm_va_block_exit(void);

// Allocates and initializes the block. The block's ref count is initialized to
// 1. The caller is responsible for inserting the block into its parent
// va_range.
//
// The caller must be holding the VA space lock in at least read mode.
//
// The va_range must have type UVM_VA_RANGE_TYPE_MANAGED.
NV_STATUS uvm_va_block_create(uvm_va_range_t *va_range,
                              NvU64 start,
                              NvU64 end,
                              uvm_va_block_t **out_block);

// Internal function called only when uvm_va_block_release drops the ref count
// to 0. Do not call directly.
void uvm_va_block_destroy(nv_kref_t *kref);

static inline void uvm_va_block_retain(uvm_va_block_t *va_block)
{
    nv_kref_get(&va_block->kref);
}

// Locking: The va_block lock must not be held.
// The va_space lock must be held in write mode unless it is the special case
// that the block has no GPU state; for example, right after calling
// uvm_va_block_create(). In that case, the va_space lock can be held in read
// mode.
static inline void uvm_va_block_release(uvm_va_block_t *va_block)
{
    if (va_block) {
        // The calling thread shouldn't be holding the block's mutex when
        // releasing the block as it might get destroyed.
        uvm_assert_unlocked_order(UVM_LOCK_ORDER_VA_BLOCK);
        nv_kref_put(&va_block->kref, uvm_va_block_destroy);
    }
}

// Same as uvm_va_block_release but the caller may be holding the VA block lock.
// The caller must ensure that the refcount will not get to zero in this call.
static inline void uvm_va_block_release_no_destroy(uvm_va_block_t *va_block)
{
    int destroyed = nv_kref_put(&va_block->kref, uvm_va_block_destroy);
    UVM_ASSERT(!destroyed);
}

// Returns true if the block is managed by HMM.
// Locking: This can be called while holding either the block lock or just the
// VA space lock in read mode, since it can only change when the VA space lock
// is held in write mode.
static inline bool uvm_va_block_is_hmm(uvm_va_block_t *va_block)
{
#if UVM_IS_CONFIG_HMM()
    return va_block->hmm.va_space;
#else
    return false;
#endif
}

// Return true if the block is dead.
// Locking: This can be called while holding either the block lock or just the
// VA space lock in read mode, since it can only change when the VA space lock
// is held in write mode.
static inline bool uvm_va_block_is_dead(uvm_va_block_t *va_block)
{
    if (va_block->va_range)
        return false;

#if UVM_IS_CONFIG_HMM()
    if (va_block->hmm.va_space)
        return false;
#endif

    return true;
}

static inline uvm_va_block_gpu_state_t *uvm_va_block_gpu_state_get(uvm_va_block_t *va_block, uvm_gpu_id_t gpu_id)
{
    return va_block->gpus[uvm_id_gpu_index(gpu_id)];
}

// Return the va_space pointer of the given block or NULL if the block is dead.
// Locking: This can be called while holding either the block lock or just the
// VA space lock in read mode, since it can only change when the VA space lock
// is held in write mode.
uvm_va_space_t *uvm_va_block_get_va_space_maybe_dead(uvm_va_block_t *va_block);

// Return the va_space pointer of the given block assuming the block is not dead
// (asserts that it is not dead and asserts va_space is not NULL).
// Locking: This can be called while holding either the block lock or just the
// VA space lock in read mode, since it can only change when the VA space lock
// is held in write mode.
uvm_va_space_t *uvm_va_block_get_va_space(uvm_va_block_t *va_block);

// Return true if the VA space has access counter migrations enabled and should
// remote map pages evicted to system memory. This is OK since access counters
// can pull the data back to vidmem if sufficient accesses trigger a migration.
// The caller must ensure that the VA space cannot go away.
bool uvm_va_space_map_remote_on_eviction(uvm_va_space_t *va_space);

// Dynamic cache-based allocation for uvm_va_block_context_t.
//
// See uvm_va_block_context_init() for a description of the mm parameter.
uvm_va_block_context_t *uvm_va_block_context_alloc(struct mm_struct *mm);
void uvm_va_block_context_free(uvm_va_block_context_t *va_block_context);

// Initialization of an already-allocated uvm_va_block_context_t.
//
// mm is used to initialize the value of va_block_context->mm. NULL is allowed.
static void uvm_va_block_context_init(uvm_va_block_context_t *va_block_context, struct mm_struct *mm)
{
    UVM_ASSERT(va_block_context);

    // Write garbage into the VA Block context to ensure that the UVM code
    // clears masks appropriately
    if (UVM_IS_DEBUG())
        memset(va_block_context, 0xff, sizeof(*va_block_context));

    va_block_context->mm = mm;
#if UVM_IS_CONFIG_HMM()
    va_block_context->hmm.vma = NULL;
#endif
}

// Check that a single policy covers the given region for the given va_block.
// This always returns true and is intended to only be used with UVM_ASSERT().
// Locking: the va_block lock must be held.
bool uvm_va_block_check_policy_is_valid(uvm_va_block_t *va_block,
                                        const uvm_va_policy_t *policy,
                                        uvm_va_block_region_t region);

// TODO: Bug 1766480: Using only page masks instead of a combination of regions
//       and page masks could simplify the below APIs and their implementations
//       at the cost of having to scan the whole mask for small regions.
//       Investigate the performance effects of doing that.

// Moves the physical pages of the given region onto the destination processor.
// If page_mask is non-NULL, the movement is further restricted to only those
// pages in the region which are present in the mask.
//
// prefetch_page_mask may be passed as a subset of page_mask when cause is
// UVM_MAKE_RESIDENT_CAUSE_REPLAYABLE_FAULT,
// UVM_MAKE_RESIDENT_CAUSE_NON_REPLAYABLE_FAULT, or
// UVM_MAKE_RESIDENT_CAUSE_ACCESS_COUNTER to indicate pages that have been
// pulled due to automatic page prefetching heuristics. For pages in this mask,
// UVM_MAKE_RESIDENT_CAUSE_PREFETCH will be reported in migration events,
// instead.
//
// This function breaks read duplication for all given pages even if they
// don't migrate. Pages which are not resident on the destination processor
// will also be unmapped from all existing processors, be populated in the
// destination processor's memory, and copied to the new physical location.
// Any new memory will be zeroed if it is the first allocation for that page
// in the system.
//
// This function does not create any new virtual mappings.
//
// This function acquires/waits for the va_block tracker and updates that
// tracker with any new work pushed.
//
// Allocation-retry: this operation may need to perform eviction to be able to
// allocate GPU memory successfully and if that happens,
// NV_ERR_MORE_PROCESSING_REQUIRED will be returned. That also means that the
// block's lock has been unlocked and relocked as part of the call and that the
// whole sequence of operations performed under the block's lock needs to be
// attempted again. To facilitate that, the caller needs to provide the same
// va_block_retry struct for each attempt that has been initialized before the
// first attempt and needs to be deinitialized after the last one. Most callers
// can just use UVM_VA_BLOCK_LOCK_RETRY() that takes care of that for the
// caller.
//
// If dest_id is the CPU then va_block_retry can be NULL and allocation-retry of
// user memory is guaranteed not to happen. Allocation-retry of GPU page tables
// can still occur though.
//
// va_block_context must not be NULL. This function will set a bit in
// va_block_context->make_resident.pages_changed_residency for each page that
// changed residency (due to a migration or first population) as a result of the
// operation and va_block_context->make_resident.all_involved_processors for
// each processor involved in the copy. This function only sets bits in those
// masks. It is the caller's responsiblity to zero the masks or not first.
//
// va_block_context->policy must also be set by the caller for the given region.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// Notably any status other than NV_OK indicates that the block's lock might
// have been unlocked and relocked.
//
// LOCKING: The caller must hold the va_block lock.
// If va_block_context->mm != NULL, va_block_context->mm->mmap_lock must be
// held in at least read mode.
NV_STATUS uvm_va_block_make_resident(uvm_va_block_t *va_block,
                                     uvm_va_block_retry_t *va_block_retry,
                                     uvm_va_block_context_t *va_block_context,
                                     uvm_processor_id_t dest_id,
                                     uvm_va_block_region_t region,
                                     const uvm_page_mask_t *page_mask,
                                     const uvm_page_mask_t *prefetch_page_mask,
                                     uvm_make_resident_cause_t cause);

// Similar to uvm_va_block_make_resident (read documentation there). The main
// differences are:
// - Pages are copied not moved (i.e. other copies of the page are not
//   unmapped)
// - Processors with a resident copy of pages that migrated have write and
//   atomic access permission revoked, unlike in uvm_va_block_make_resident
//   where they are unmapped
// - All remote mappings (due to either SetAccessedBy or performance heuristics)
//   are broken
// - Only managed va_blocks are supported.
//   TODO: Bug 3660922: need to implement HMM read duplication support.
NV_STATUS uvm_va_block_make_resident_read_duplicate(uvm_va_block_t *va_block,
                                                    uvm_va_block_retry_t *va_block_retry,
                                                    uvm_va_block_context_t *va_block_context,
                                                    uvm_processor_id_t dest_id,
                                                    uvm_va_block_region_t region,
                                                    const uvm_page_mask_t *page_mask,
                                                    const uvm_page_mask_t *prefetch_page_mask,
                                                    uvm_make_resident_cause_t cause);

// Similar to uvm_va_block_make_resident() (read documentation there). The
// difference is that source pages are only copied to the destination and the
// residency is not updated until uvm_va_block_make_resident_finish() is called.
// Otherwise, the combination of uvm_va_block_make_resident_copy() and
// uvm_va_block_make_resident_finish() is the same as just calling
// uvm_va_block_make_resident(). Note, however, that the va_block lock must be
// held across the two calls for the operation to be complete. The va_block
// lock can be dropped after calling uvm_va_block_make_resident_copy() but
// uvm_va_block_make_resident_copy() must be called again after relocking the
// va_block lock and before calling uvm_va_block_make_resident_finish().
// This split is needed when using migrate_vma_setup() and migrate_vma_pages()
// so that when migrate_vma_pages() indicates a page is not migrating, the
// va_block state is not updated.
// LOCKING: The caller must hold the va_block lock.
NV_STATUS uvm_va_block_make_resident_copy(uvm_va_block_t *va_block,
                                          uvm_va_block_retry_t *va_block_retry,
                                          uvm_va_block_context_t *va_block_context,
                                          uvm_processor_id_t dest_id,
                                          uvm_va_block_region_t region,
                                          const uvm_page_mask_t *page_mask,
                                          const uvm_page_mask_t *prefetch_page_mask,
                                          uvm_make_resident_cause_t cause);

// The page_mask must be the same or a subset of the page_mask passed to
// uvm_va_block_make_resident_copy(). This step updates the residency and breaks
// read duplication.
// LOCKING: The caller must hold the va_block lock.
void uvm_va_block_make_resident_finish(uvm_va_block_t *va_block,
                                       uvm_va_block_context_t *va_block_context,
                                       uvm_va_block_region_t region,
                                       const uvm_page_mask_t *page_mask);

// Creates or upgrades a mapping from the input processor to the given virtual
// address region. Pages which already have new_prot permissions or higher are
// skipped, so this call ensures that the range is mapped with at least new_prot
// permissions. new_prot must not be UVM_PROT_NONE. uvm_va_block_unmap or
// uvm_va_block_revoke_prot should be used to downgrade permissions instead.
//
// The mapped pages are described by the region parameter and the map page mask
// that allows the caller to restrict the map operation to specific pages within
// the region. If the page mask is NULL then the whole region is mapped.
//
// If the input processor is a GPU with no GPU VA space registered, or if the
// input processor is the CPU and this thread is not allowed to create CPU
// mappings, this function does nothing. CPU mappings are only allowed if
// uvm_va_range_vma_check(va_block_context->mm) is valid, so the caller must
// set va_block_context->mm before calling this function.
//
// cause specifies the cause to be reported in events in case a remote mapping
// is created.
//
// Any CPU mappings will wait for the va_block tracker. If this function pushes
// GPU work it will first acquire the va_block tracker, then add the pushed work
// to out_tracker. It is the caller's responsibility to add this work to
// va_block's tracker. Note that while it is generally safe to run map
// operations on different GPUs concurrently, two PTE operations (map, unmap,
// revoke) on the same GPU must be serialized even if they target different
// pages because the earlier operation can cause a PTE split or merge which is
// assumed by the later operation.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the entries in the
// out_tracker were added to the block's tracker and then the block's lock was
// unlocked and relocked.
//
// In general, any status other than NV_OK indicates that the block's lock might
// have been unlocked and relocked.
//
// LOCKING: The caller must hold the va block lock. If va_block_context->mm !=
//          NULL, va_block_context->mm->mmap_lock must be held in at least read
//          mode.
NV_STATUS uvm_va_block_map(uvm_va_block_t *va_block,
                           uvm_va_block_context_t *va_block_context,
                           uvm_processor_id_t id,
                           uvm_va_block_region_t region,
                           const uvm_page_mask_t *map_page_mask,
                           uvm_prot_t new_prot,
                           UvmEventMapRemoteCause cause,
                           uvm_tracker_t *out_tracker);

// Like uvm_va_block_map, except it maps all processors in the input mask. The
// VA block tracker contains all map operations on return.
//
// Note that this can return NV_ERR_MORE_PROCESSING_REQUIRED just like
// uvm_va_block_map() indicating that the operation needs to be retried.
NV_STATUS uvm_va_block_map_mask(uvm_va_block_t *va_block,
                                uvm_va_block_context_t *va_block_context,
                                const uvm_processor_mask_t *map_processor_mask,
                                uvm_va_block_region_t region,
                                const uvm_page_mask_t *map_page_mask,
                                uvm_prot_t new_prot,
                                UvmEventMapRemoteCause cause);

// Unmaps virtual regions from a single processor. This does not free page
// tables or physical memory. This is safe to call on the eviction path, but the
// caller must ensure that the block hasn't been killed.
//
// The unmapped pages are described by the region parameter and the unmap page
// mask that allows the caller to restrict the unmap operation to specific pages
// within the region. If the page mask is NULL then the whole region is
// unmapped.
//
// If id is UVM_ID_CPU, this is guaranteed to return NV_OK, and this is safe to
// call without holding a reference on the mm which owns the associated vma.
//
// Any CPU unmappings will wait for the va_block tracker. If this function
// pushes GPU work it will first acquire the va_block tracker, then add the
// pushed work to out_tracker. It is the caller's responsibility to add this
// work to va_block's tracker. Note that while it is generally safe to run unmap
// operations on different GPUs concurrently, two PTE operations (map, unmap,
// revoke) on the same GPU must be serialized even if they target different
// pages because the earlier operation can cause a PTE split or merge which is
// assumed by the later operation.
//
// va_block_context must not be NULL. The va_block_context->policy is unused.
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the entries in the
// out_tracker were added to the block's tracker and then the block's lock was
// unlocked and relocked. It is guaranteed that retry will not be required if
// the unmap does not cause a PTE split. Examples of operations which will not
// cause a PTE split include unmapping the entire block, unmapping all PTEs with
// matching attributes, and unmapping all PTEs which point to the same physical
// chunk.
//
// LOCKING: The caller must hold the va_block lock.
NV_STATUS uvm_va_block_unmap(uvm_va_block_t *va_block,
                             uvm_va_block_context_t *va_block_context,
                             uvm_processor_id_t id,
                             uvm_va_block_region_t region,
                             const uvm_page_mask_t *unmap_page_mask,
                             uvm_tracker_t *out_tracker);

// Like uvm_va_block_unmap, except it unmaps all processors in the input mask.
// The VA block tracker contains all map operations on return.
NV_STATUS uvm_va_block_unmap_mask(uvm_va_block_t *va_block,
                                  uvm_va_block_context_t *va_block_context,
                                  const uvm_processor_mask_t *unmap_processor_mask,
                                  uvm_va_block_region_t region,
                                  const uvm_page_mask_t *unmap_page_mask);

// Function called when the preferred location changes. Notably:
// - Mark all CPU pages as dirty because the new processor may not have
//   up-to-date data.
// - Unmap the preferred location's processor from any pages in this region
//   which are not resident on the preferred location.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: The caller must hold the VA block lock.
NV_STATUS uvm_va_block_set_preferred_location_locked(uvm_va_block_t *va_block,
                                                     uvm_va_block_context_t *va_block_context,
                                                     uvm_va_block_region_t region);

// Maps the given processor to all resident pages in this block, as allowed by
// location and policy. Waits for the operation to complete before returning.
// This function should only be called with managed va_blocks.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: This takes and releases the VA block lock. If va_block_context->mm
//          != NULL, va_block_context->mm->mmap_lock must be held in at least
//          read mode.
NV_STATUS uvm_va_block_set_accessed_by(uvm_va_block_t *va_block,
                                       uvm_va_block_context_t *va_block_context,
                                       uvm_processor_id_t processor_id);

// Maps given processor to all resident pages in this block and region, as
// allowed by location and policy. The caller is responsible for waiting for
// the tracker after all mappings have been started.
// This function can be called with HMM and managed va_blocks.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: The caller must hold the va_block lock and
//          va_block_context->mm->mmap_lock must be held in at least read mode.
NV_STATUS uvm_va_block_set_accessed_by_locked(uvm_va_block_t *va_block,
                                              uvm_va_block_context_t *va_block_context,
                                              uvm_processor_id_t processor_id,
                                              uvm_va_block_region_t region,
                                              uvm_tracker_t *out_tracker);

// Breaks SetAccessedBy and remote mappings
// This function should only be called with managed va_blocks.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: This takes and releases the VA block lock. If va_block_context->mm
//          != NULL, va_block_context->mm->mmap_lock must be held in at least
//          read mode.
NV_STATUS uvm_va_block_set_read_duplication(uvm_va_block_t *va_block,
                                            uvm_va_block_context_t *va_block_context);

// Restores SetAccessedBy mappings
// This function should only be called with managed va_blocks.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: This takes and releases the VA block lock. If va_block_context->mm
//          != NULL, va_block_context->mm->mmap_lock must be held in at least
//          read mode.
NV_STATUS uvm_va_block_unset_read_duplication(uvm_va_block_t *va_block,
                                              uvm_va_block_context_t *va_block_context);

// Check if processor_id is allowed to access the va_block with access_type
// permissions. Return values:
//
// NV_ERR_INVALID_ADDRESS       The VA block is logically dead (zombie)
// NV_ERR_INVALID_ACCESS_TYPE   The vma corresponding to the VA range does not
//                              allow access_type permissions, or migration is
//                              disallowed and processor_id cannot access the
//                              range remotely (UVM-Lite).
// NV_ERR_INVALID_OPERATION     The access would violate the policies specified
//                              by UvmPreventMigrationRangeGroups.
//
// va_block_context must not be NULL, va_block_context->policy must be valid,
// and if the va_block is a HMM block, va_block_context->hmm.vma must be valid
// which also means the va_block_context->mm is not NULL, retained, and locked
// for at least read.
// Locking: the va_block lock must be held.
NV_STATUS uvm_va_block_check_logical_permissions(uvm_va_block_t *va_block,
                                                 uvm_va_block_context_t *va_block_context,
                                                 uvm_processor_id_t processor_id,
                                                 uvm_page_index_t page_index,
                                                 uvm_fault_type_t access_type,
                                                 bool allow_migration);

// API for access privilege revocation
//
// Revoke prot_to_revoke access permissions for the given processor.
//
// The revoked pages are described by the region parameter and the revoke page
// mask that allows the caller to restrict the revoke operation to specific
// pages within the region.
//
// prot_to_revoke must be greater than UVM_PROT_READ_ONLY. Caller should call
// unmap explicitly if it wants to revoke all access privileges.
//
// If id is UVM_ID_CPU, and prot_to_revoke is UVM_PROT_READ_WRITE_ATOMIC, no
// action is performed. If the processor id corresponds to the CPU and the
// caller cannot establish CPU mappings because it does not have a reference on
// vma->vm_mm (va_block_context->mm != vma->vm_mm), the page will be simply
// unmapped. Caller should call unmap explicitly if it wants to revoke all
// access privileges.
//
// Any CPU revocation will wait for the va_block tracker. If this function
// pushes GPU work it will first acquire the va_block tracker, then add the
// pushed work to out_tracker. It is the caller's responsibility to add this
// work to va_block's tracker. Note that while it is generally safe to run
// revocation operations on different GPUs concurrently, two PTE operations
// (map, unmap, revoke) on the same GPU must be serialized even if they target
// different pages because the earlier operation can cause a PTE split or merge
// which is assumed by the later operation.
//
// va_block_context must not be NULL. The va_block_context->policy is unused.
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the entries in the
// out_tracker were added to the block's tracker and then the block's lock was
// unlocked and relocked.
//
// In general, any status other than NV_OK indicates that the block's lock might
// have been unlocked and relocked.
//
// LOCKING: The caller must hold the va block lock. If va_block_context->mm !=
//          NULL, va_block_context->mm->mmap_lock must be held in at least read
//          mode.
NV_STATUS uvm_va_block_revoke_prot(uvm_va_block_t *va_block,
                                   uvm_va_block_context_t *va_block_context,
                                   uvm_processor_id_t id,
                                   uvm_va_block_region_t region,
                                   const uvm_page_mask_t *revoke_page_mask,
                                   uvm_prot_t prot_to_revoke,
                                   uvm_tracker_t *out_tracker);

// Like uvm_va_block_revoke_prot(), except it revokes all processors in the
// input mask. The VA block tracker contains all revocation operations on
// return.
//
// Note that this can return NV_ERR_MORE_PROCESSING_REQUIRED just like
// uvm_va_block_revoke_prot() indicating that the operation needs to be retried.
NV_STATUS uvm_va_block_revoke_prot_mask(uvm_va_block_t *va_block,
                                        uvm_va_block_context_t *va_block_context,
                                        const uvm_processor_mask_t *revoke_processor_mask,
                                        uvm_va_block_region_t region,
                                        const uvm_page_mask_t *revoke_page_mask,
                                        uvm_prot_t prot_to_revoke);

// Tries to map all pages in the given region and map_page_mask with at most
// max_prot privileges for appropriate processors as determined by the
// accessed_by mask, heuristics and the given processor mask (excluding
// processor_id, which triggered the migration and should have already been
// mapped).
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// This function acquires/waits for the va_block tracker and updates that
// tracker with any new work pushed.
//
// Note that this can return NV_ERR_MORE_PROCESSING_REQUIRED just like
// uvm_va_block_map() indicating that the operation needs to be retried.
//
// LOCKING: The caller must hold the va block lock. If va_block_context->mm !=
//          NULL, va_block_context->mm->mmap_lock must be held in at least read
//          mode.
NV_STATUS uvm_va_block_add_mappings_after_migration(uvm_va_block_t *va_block,
                                                    uvm_va_block_context_t *va_block_context,
                                                    uvm_processor_id_t new_residency,
                                                    uvm_processor_id_t processor_id,
                                                    uvm_va_block_region_t region,
                                                    const uvm_page_mask_t *map_page_mask,
                                                    uvm_prot_t max_prot,
                                                    const uvm_processor_mask_t *processor_mask);

// Maps processors using SetAccessedBy to all resident pages in the region
// parameter. On Volta+ it is also used to map evicted pages that can be later
// pulled back by using access counters.
//
// This function acquires/waits for the va_block tracker and updates that
// tracker with any new work pushed.
//
// Note that this can return NV_ERR_MORE_PROCESSING_REQUIRED just like
// uvm_va_block_map() indicating that the operation needs to be retried.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
//
// LOCKING: The caller must hold the va block lock. If va_block_context->mm !=
//          NULL, va_block_context->mm->mmap_lock must be held in at least read
//          mode.
NV_STATUS uvm_va_block_add_mappings(uvm_va_block_t *va_block,
                                    uvm_va_block_context_t *va_block_context,
                                    uvm_processor_id_t processor_id,
                                    uvm_va_block_region_t region,
                                    const uvm_page_mask_t *page_mask,
                                    UvmEventMapRemoteCause cause);

// Notifies the VA block that a new GPU VA space has been created.
// LOCKING: The caller must hold the va_block lock
NV_STATUS uvm_va_block_add_gpu_va_space(uvm_va_block_t *va_block, uvm_gpu_va_space_t *gpu_va_space);

// Destroys the VA block's mappings and page tables on the GPU, if it has any.
//
// If mm != NULL, that mm is used for any CPU mappings which may be created as
// a result of this call. See uvm_va_block_context_t::mm for details.
//
// va_block_context must not be NULL. The va_block_context->policy is unused.
//
// LOCKING: The caller must hold the va_block lock. If block_context->mm is not
// NULL, the caller must hold mm->mmap_lock in at least read mode.
void uvm_va_block_remove_gpu_va_space(uvm_va_block_t *va_block,
                                      uvm_gpu_va_space_t *gpu_va_space,
                                      uvm_va_block_context_t *block_context);

// Creates any mappings necessary in this VA block between the two GPUs, in
// either direction.
// LOCKING: The caller must hold the va_block lock
NV_STATUS uvm_va_block_enable_peer(uvm_va_block_t *va_block, uvm_gpu_t *gpu0, uvm_gpu_t *gpu1);

// Unmaps all page tables in this VA block which have peer mappings between
// the two GPUs, in either direction.
// LOCKING: The caller must hold the va_block lock
void uvm_va_block_disable_peer(uvm_va_block_t *va_block, uvm_gpu_t *gpu0, uvm_gpu_t *gpu1);

// Unmap any mappings from GPU to the preferred location.
//
// The GPU has to be in UVM-Lite mode.
//
// LOCKING: The caller must hold the va_block lock
void uvm_va_block_unmap_preferred_location_uvm_lite(uvm_va_block_t *va_block, uvm_gpu_t *gpu);

// Frees all memory under this block associated with this GPU. Any portion of
// the block which is resident on the GPU is evicted to sysmem before being
// freed.
//
// If mm != NULL, that mm is used for any CPU mappings which may be created as
// a result of this call. See uvm_va_block_context_t::mm for details.
//
// LOCKING: This takes and releases the VA block lock. If mm != NULL, the caller
//          must hold mm->mmap_lock in at least read mode.
void uvm_va_block_unregister_gpu(uvm_va_block_t *va_block, uvm_gpu_t *gpu, struct mm_struct *mm);

// Same as uvm_va_block_unregister_gpu() but the VA block lock must be held.
// Note that this handles allocation-retry internally and hence might unlock
// and relock block's lock.
void uvm_va_block_unregister_gpu_locked(uvm_va_block_t *va_block, uvm_gpu_t *gpu, struct mm_struct *mm);

// Unmaps all memory associated with the block and drops the ref count of the
// block. This allows the caller to free resources associated with this block
// regardless of the block's current ref count. Most importantly it allows the
// VA covered by this block to be immediately available for other page table
// mappings upon return.
//
// This clears block->va_range, so only the VA range destroy path should call
// it. Other paths with references on this block, specifically the eviction path
// which temporarily takes a reference to the block, must always check the block
// state after taking the block lock to see if their mapping is still in place.
//
// All of the unmap and state destruction steps are also performed when the ref
// count goes to 0, so this function only needs to be called if the block's
// resources need to be reclaimed immediately.
//
// The caller should not lock the block before calling this function.
//
// This performs a uvm_va_block_release.
void uvm_va_block_kill(uvm_va_block_t *va_block);

// Exactly the same split semantics as uvm_va_range_split, including error
// handling. See that function's comments for details.
//
// new_va_block's va_range is set to new_va_range before any reverse mapping is
// established to the new block, but the caller is responsible for inserting the
// new block into the range.
NV_STATUS uvm_va_block_split(uvm_va_block_t *existing_va_block,
                             NvU64 new_end,
                             uvm_va_block_t **new_va_block,
                             uvm_va_range_t *new_va_range);

// Exactly the same split semantics as uvm_va_block_split, including error
// handling except the existing_va_block block lock needs to be held and
// the new_va_block has to be preallocated.
// Also note that the existing_va_block lock may be dropped and re-acquired.
NV_STATUS uvm_va_block_split_locked(uvm_va_block_t *existing_va_block,
                                    NvU64 new_end,
                                    uvm_va_block_t *new_va_block,
                                    uvm_va_range_t *new_va_range);

// Handles a CPU fault in the given VA block, performing any operations
// necessary to establish a coherent CPU mapping (migrations, cache invalidates,
// etc.).
//
// Locking:
//  - vma->vm_mm->mmap_lock must be held in at least read mode. Note, that
//    might not be the same as current->mm->mmap_lock.
//  - va_space lock must be held in at least read mode
//
// service_context->block_context.mm is ignored and vma->vm_mm is used instead.
// service_context->block_context.policy is set by this function.
//
// Returns NV_ERR_INVALID_ACCESS_TYPE if a CPU mapping to fault_addr cannot be
// accessed, for example because it's within a range group which is non-
// migratable.
NV_STATUS uvm_va_block_cpu_fault(uvm_va_block_t *va_block,
                                 NvU64 fault_addr,
                                 bool is_write,
                                 uvm_service_block_context_t *service_context);

// Performs any operations necessary to establish a coherent mapping
// (migrations, cache invalidates, etc.) in response to the given service block
// context.
//
// service_context must not be NULL and service_context->block_context.policy
// must be valid. See the comments for uvm_va_block_check_policy_is_valid().
// If va_block is a HMM block, va_block_context->hmm.vma must be valid.
// See the comments for uvm_hmm_check_context_vma_is_valid() in uvm_hmm.h.
// service_context->prefetch_hint is set by this function.
//
// Locking:
//  - service_context->block_context.mm->mmap_lock must be held in at least
//    read mode, if valid.
//  - va_space lock must be held in at least read mode
//  - va_block lock must be held
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the block's lock
// was unlocked and relocked.
//
// NV_WARN_MORE_PROCESSING_REQUIRED indicates that thrashing has been detected
// and the performance heuristics logic decided to throttle execution.
// Any other error code different than NV_OK indicates OOM or a global fatal
// error.
NV_STATUS uvm_va_block_service_locked(uvm_processor_id_t processor_id,
                                      uvm_va_block_t *va_block,
                                      uvm_va_block_retry_t *block_retry,
                                      uvm_service_block_context_t *service_context);

// Performs population of the destination pages, unmapping and copying source
// pages to new_residency.
//
// service_context must not be NULL and service_context->block_context.policy
// must be valid. See the comments for uvm_va_block_check_policy_is_valid().
// If va_block is a HMM block, va_block_context->hmm.vma must be valid.
// See the comments for uvm_hmm_check_context_vma_is_valid() in uvm_hmm.h.
// service_context->prefetch_hint should be set before calling this function.
//
// Locking:
//  - service_context->block_context.mm->mmap_lock must be held in at least
//    read mode, if valid.
//  - va_space lock must be held in at least read mode
//  - va_block lock must be held
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the block's lock
// was unlocked and relocked.
//
// NV_WARN_MORE_PROCESSING_REQUIRED indicates that thrashing has been detected
// and the performance heuristics logic decided to throttle execution.
// Any other error code different than NV_OK indicates OOM or a global fatal
// error.
NV_STATUS uvm_va_block_service_copy(uvm_processor_id_t processor_id,
                                    uvm_processor_id_t new_residency,
                                    uvm_va_block_t *va_block,
                                    uvm_va_block_retry_t *block_retry,
                                    uvm_service_block_context_t *service_context);

// This updates the va_block residency state and maps the faulting processor_id
// to the new residency (which may be remote).
//
// service_context must not be NULL and service_context->block_context.policy
// must be valid. See the comments for uvm_va_block_check_policy_is_valid().
// If va_block is a HMM block, va_block_context->hmm.vma must be valid.
// See the comments for uvm_hmm_check_context_vma_is_valid() in uvm_hmm.h.
// service_context must be initialized by calling uvm_va_block_service_copy()
// before calling this function.
//
// Locking:
//  - service_context->block_context.mm->mmap_lock must be held in at least
//    read mode, if valid.
//  - va_space lock must be held in at least read mode
//  - va_block lock must be held
//  - the mmap lock and va_space lock must be held across the calls to
//    uvm_va_block_service_copy() and this function. If the va_block lock is
//    dropped inbetween, special care is needed to check for eviction and
//    invalidation callbacks.
//
// If allocation-retry was required as part of the operation and was successful,
// NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case, the block's lock
// was unlocked and relocked.
//
// NV_WARN_MORE_PROCESSING_REQUIRED indicates that thrashing has been detected
// and the performance heuristics logic decided to throttle execution.
// Any other error code different than NV_OK indicates OOM or a global fatal
// error.
NV_STATUS uvm_va_block_service_finish(uvm_processor_id_t processor_id,
                                      uvm_va_block_t *va_block,
                                      uvm_service_block_context_t *service_context);

// Allocate GPU state for the given va_block and registered GPUs.
// Locking: The block lock must be held.
NV_STATUS uvm_va_block_gpu_state_alloc(uvm_va_block_t *va_block);

// Release any GPU or policy data associated with the given region in response
// to munmap().
// Locking: The va_block lock must be held.
void uvm_va_block_munmap_region(uvm_va_block_t *va_block,
                                uvm_va_block_region_t region);

// Size of the block in bytes. Guaranteed to be a page-aligned value between
// PAGE_SIZE and UVM_VA_BLOCK_SIZE.
static inline NvU64 uvm_va_block_size(uvm_va_block_t *block)
{
    NvU64 size = block->end - block->start + 1;
    UVM_ASSERT(PAGE_ALIGNED(size));
    UVM_ASSERT(size >= PAGE_SIZE);
    UVM_ASSERT(size <= UVM_VA_BLOCK_SIZE);
    return size;
}

// Number of pages with PAGE_SIZE in the block
static inline size_t uvm_va_block_num_cpu_pages(uvm_va_block_t *block)
{
    return uvm_va_block_size(block) / PAGE_SIZE;
}

// VA of the given page using CPU page size. page_index must be valid
static inline NvU64 uvm_va_block_cpu_page_address(uvm_va_block_t *block, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < uvm_va_block_num_cpu_pages(block));
    return block->start + PAGE_SIZE * page_index;
}

// Get the physical address on the given GPU for given residency
uvm_gpu_phys_address_t uvm_va_block_res_phys_page_address(uvm_va_block_t *va_block,
                                                          uvm_page_index_t page_index,
                                                          uvm_processor_id_t residency,
                                                          uvm_gpu_t *gpu);

// Get the page physical address on the given GPU
//
// This will assert that GPU state is indeed present.
uvm_gpu_phys_address_t uvm_va_block_gpu_phys_page_address(uvm_va_block_t *va_block,
                                                          uvm_page_index_t page_index,
                                                          uvm_gpu_t *gpu);

static bool uvm_va_block_contains_address(uvm_va_block_t *block, NvU64 address)
{
    return address >= block->start && address <= block->end;
}

// Obtain a pointer to the uvm_va_block_test_t structure for the given VA
// block. If uvm_enable_builtin_tests is unset, NULL will be returned.
static uvm_va_block_test_t *uvm_va_block_get_test(uvm_va_block_t *va_block)
{
    if (uvm_enable_builtin_tests)
        return &container_of(va_block, uvm_va_block_wrapper_t, block)->test;

    return NULL;
}

// Get the page residency mask for a processor if it's known to be there.
//
// If the processor is a GPU, this will assert that GPU state is indeed present.
uvm_page_mask_t *uvm_va_block_resident_mask_get(uvm_va_block_t *block, uvm_processor_id_t processor);

// Get the page mapped mask for a processor. The returned mask cannot be
// directly modified by the caller
//
// If the processor is a GPU, this will assert that GPU state is indeed present.
const uvm_page_mask_t *uvm_va_block_map_mask_get(uvm_va_block_t *block, uvm_processor_id_t processor);

// VA block lookup functions. There are a number of permutations which might be
// useful, such as looking up the block from {va_space, va_range} x {addr,
// block index}. The ones implemented here and in uvm_va_range.h support the
// primary three use cases, which are:
// 1) Iterating over all VA blocks in a VA range. This uses block indices on the
//    VA range:
//      uvm_va_range_num_blocks
//      uvm_va_range_block_index
//      uvm_va_range_block
//      uvm_va_range_block_create
// 2) Operating on a single VA block (fault). This looks up the block using the
//    VA space and address:
//      uvm_va_block_find
//      uvm_va_block_find_create
// 3) Operating on a single VA block (fault). This looks up the block using the
//    supplied VA range and address:
//      uvm_va_block_find_create_in_range

// Finds the UVM or HMM VA block containing addr, if any. The va_space->lock
// must be held in at least read mode. Return values:
// NV_ERR_INVALID_ADDRESS   addr is not a UVM_VA_RANGE_TYPE_MANAGED va_range nor
//                          a HMM enabled VMA.
//
// NV_ERR_OBJECT_NOT_FOUND  addr is valid but no block has been allocated to
//                          cover it yet
//
// NV_OK                    The block was returned successfully
NV_STATUS uvm_va_block_find(uvm_va_space_t *va_space, NvU64 addr, uvm_va_block_t **out_block);

// Same as uvm_va_block_find except that the block is created if not found.
// If addr is covered by a UVM_VA_RANGE_TYPE_MANAGED va_range, a managed block
// will be created. Otherwise, if addr is not covered by any va_range, HMM is
// enabled in the va_space, and va_block_context and va_block_context->mm are
// non-NULL, then a HMM block will be created and va_block_context->hmm.vma is
// set to the VMA covering 'addr'. The va_block_context->policy field is left
// unchanged.
// In either case, if va_block_context->mm is non-NULL, it must be retained and
// locked in at least read mode. Return values:
// NV_ERR_INVALID_ADDRESS   addr is not a UVM_VA_RANGE_TYPE_MANAGED va_range nor
//                          a HMM enabled VMA.
// NV_ERR_NO_MEMORY         memory could not be allocated.
NV_STATUS uvm_va_block_find_create(uvm_va_space_t *va_space,
                                   NvU64 addr,
                                   uvm_va_block_context_t *va_block_context,
                                   uvm_va_block_t **out_block);

// Same as uvm_va_block_find_create except that va_range lookup was already done
// by the caller. If the supplied va_range is NULL, this function behaves just
// like when the va_range lookup in uvm_va_block_find_create is NULL.
NV_STATUS uvm_va_block_find_create_in_range(uvm_va_space_t *va_space,
                                            uvm_va_range_t *va_range,
                                            NvU64 addr,
                                            uvm_va_block_context_t *va_block_context,
                                            uvm_va_block_t **out_block);

// Same as uvm_va_block_find_create except that only managed va_blocks are
// created if not already present in the VA range.
static NV_STATUS uvm_va_block_find_create_managed(uvm_va_space_t *va_space,
                                                  NvU64 addr,
                                                  uvm_va_block_t **out_block)
{
    return uvm_va_block_find_create(va_space, addr, NULL, out_block);
}

// Look up a chunk backing a specific address within the VA block.
// Returns NULL if none.
uvm_gpu_chunk_t *uvm_va_block_lookup_gpu_chunk(uvm_va_block_t *va_block, uvm_gpu_t *gpu, NvU64 address);

// Implementation of the UvmMigrate() API at the VA block scope.
//
// The out_tracker can be NULL.
//
// If do_mappings is false, mappings are not added after pages have been
// migrated.
//
// The caller needs to handle allocation-retry. va_block_retry can be NULL if
// the destination is the CPU.
//
// va_block_context must not be NULL and va_block_context->policy must be valid.
// See the comments for uvm_va_block_check_policy_is_valid().
// If va_block is a HMM block, va_block_context->hmm.vma must be valid.
// See the comments for uvm_hmm_check_context_vma_is_valid() in uvm_hmm.h.
//
// LOCKING: The caller must hold the va_block lock. If va_block_context->mm !=
//          NULL, va_block_context->mm->mmap_lock must be held in at least
//          read mode.
NV_STATUS uvm_va_block_migrate_locked(uvm_va_block_t *va_block,
                                      uvm_va_block_retry_t *va_block_retry,
                                      uvm_va_block_context_t *va_block_context,
                                      uvm_va_block_region_t region,
                                      uvm_processor_id_t dest_id,
                                      uvm_migrate_mode_t mode,
                                      uvm_tracker_t *out_tracker);

// Write block's data from a CPU buffer
//
// The [dst, dst + size) range has to fit within a single PAGE_SIZE page.
//
// va_block_context must not be NULL. The caller is not required to set
// va_block_context->policy or va_block_context->hmm.vma.
//
// The caller needs to support allocation-retry of page tables.
//
// LOCKING: The caller must hold the va_block lock
NV_STATUS uvm_va_block_write_from_cpu(uvm_va_block_t *va_block,
                                      uvm_va_block_context_t *block_context,
                                      NvU64 dst,
                                      uvm_mem_t *src,
                                      size_t size);

// Read block's data into a CPU buffer
//
// The [src, src + size) range has to fit within a single PAGE_SIZE page.
//
// LOCKING: The caller must hold the va_block lock
NV_STATUS uvm_va_block_read_to_cpu(uvm_va_block_t *va_block, uvm_mem_t *dst, NvU64 src, size_t size);

// Initialize va block retry tracking
void uvm_va_block_retry_init(uvm_va_block_retry_t *uvm_va_block_retry);

// Deinitialize va block retry tracking after a block operation
//
// Frees all the remaining free chunks and unpins all the used chunks.
void uvm_va_block_retry_deinit(uvm_va_block_retry_t *uvm_va_block_retry, uvm_va_block_t *va_block);

// Evict all chunks from the block that are subchunks of the passed in root_chunk.
//
// Add all the work tracking the eviction to the tracker.
//
// Returns NV_OK if the block is dead or doesn't have any subchunks of the
// root_chunk.
//
// LOCKING: The caller must hold the va_block lock
NV_STATUS uvm_va_block_evict_chunks(uvm_va_block_t *va_block,
                                    uvm_gpu_t *gpu,
                                    uvm_gpu_chunk_t *root_chunk,
                                    uvm_tracker_t *tracker);

NV_STATUS uvm_test_va_block_inject_error(UVM_TEST_VA_BLOCK_INJECT_ERROR_PARAMS *params, struct file *filp);
NV_STATUS uvm_test_change_pte_mapping(UVM_TEST_CHANGE_PTE_MAPPING_PARAMS *params, struct file *filp);
NV_STATUS uvm_test_va_block_info(UVM_TEST_VA_BLOCK_INFO_PARAMS *params, struct file *filp);
NV_STATUS uvm_test_va_residency_info(UVM_TEST_VA_RESIDENCY_INFO_PARAMS *params, struct file *filp);

// Compute the offset in system pages of addr from the start of va_block.
static uvm_page_index_t uvm_va_block_cpu_page_index(uvm_va_block_t *va_block, NvU64 addr)
{
    UVM_ASSERT(addr >= va_block->start);
    UVM_ASSERT(addr <= va_block->end);
    return (addr - va_block->start) / PAGE_SIZE;
}

// Computes the size and index in the gpu_state chunks array of the GPU chunk
// which corresponds to the given page_index of the VA region.
// Note this is only used for testing and does not work on HMM va_blocks as it
// returns incorrect results for those.
size_t uvm_va_block_gpu_chunk_index_range(NvU64 start,
                                          NvU64 size,
                                          uvm_gpu_t *gpu,
                                          uvm_page_index_t page_index,
                                          uvm_chunk_size_t *out_chunk_size);

// If there are any resident CPU pages in the block, mark them as dirty
void uvm_va_block_mark_cpu_dirty(uvm_va_block_t *va_block);

// Sets the internal state required to handle fault cancellation
//
// This function may require allocating page tables to split big pages into 4K
// pages. If allocation-retry was required as part of the operation and was
// successful, NV_ERR_MORE_PROCESSING_REQUIRED is returned. In this case the
// block's lock was unlocked and relocked.
//
// va_block_context must not be NULL. The va_block_context->policy is unused.
//
// LOCKING: The caller must hold the va_block lock.
NV_STATUS uvm_va_block_set_cancel(uvm_va_block_t *va_block, uvm_va_block_context_t *block_context, uvm_gpu_t *gpu);

//
// uvm_va_block_region_t helpers
//

static uvm_va_block_region_t uvm_va_block_region(uvm_page_index_t first, uvm_page_index_t outer)
{
    BUILD_BUG_ON(PAGES_PER_UVM_VA_BLOCK >= (1 << (sizeof(first) * 8)));

    UVM_ASSERT(first <= outer);

    return (uvm_va_block_region_t){ .first = first, .outer = outer };
}

static uvm_va_block_region_t uvm_va_block_region_for_page(uvm_page_index_t page_index)
{
    return uvm_va_block_region(page_index, page_index + 1);
}

static size_t uvm_va_block_region_num_pages(uvm_va_block_region_t region)
{
    return region.outer - region.first;
}

static NvU64 uvm_va_block_region_size(uvm_va_block_region_t region)
{
    return uvm_va_block_region_num_pages(region) * PAGE_SIZE;
}

static NvU64 uvm_va_block_region_start(uvm_va_block_t *va_block, uvm_va_block_region_t region)
{
    return va_block->start + region.first * PAGE_SIZE;
}

static NvU64 uvm_va_block_region_end(uvm_va_block_t *va_block, uvm_va_block_region_t region)
{
    return va_block->start + region.outer * PAGE_SIZE - 1;
}

static bool uvm_va_block_region_contains_region(uvm_va_block_region_t region, uvm_va_block_region_t subregion)
{
    return subregion.first >= region.first && subregion.outer <= region.outer;
}

static bool uvm_va_block_region_contains_page(uvm_va_block_region_t region, uvm_page_index_t page_index)
{
    return uvm_va_block_region_contains_region(region, uvm_va_block_region_for_page(page_index));
}

// Create a block range from a va block and start and end virtual addresses
// within the block.
static uvm_va_block_region_t uvm_va_block_region_from_start_end(uvm_va_block_t *va_block, NvU64 start, NvU64 end)
{
    uvm_va_block_region_t region;

    UVM_ASSERT(start < end);
    UVM_ASSERT(start >= va_block->start);
    UVM_ASSERT(end <= va_block->end);
    UVM_ASSERT(PAGE_ALIGNED(start));
    UVM_ASSERT(PAGE_ALIGNED(end + 1));

    region.first = uvm_va_block_cpu_page_index(va_block, start);
    region.outer = uvm_va_block_cpu_page_index(va_block, end) + 1;

    return region;
}

static uvm_va_block_region_t uvm_va_block_region_from_start_size(uvm_va_block_t *va_block, NvU64 start, NvU64 size)
{
    return uvm_va_block_region_from_start_end(va_block, start, start + size - 1);
}

static uvm_va_block_region_t uvm_va_block_region_from_block(uvm_va_block_t *va_block)
{
    return uvm_va_block_region(0, uvm_va_block_num_cpu_pages(va_block));
}

// Create a block region from a va block and page mask. Note that the region
// covers the first through the last set bit and may have unset bits in between.
static uvm_va_block_region_t uvm_va_block_region_from_mask(uvm_va_block_t *va_block, const uvm_page_mask_t *page_mask)
{
    uvm_va_block_region_t region;
    uvm_page_index_t outer = uvm_va_block_num_cpu_pages(va_block);

    region.first = find_first_bit(page_mask->bitmap, outer);
    if (region.first >= outer) {
        region = uvm_va_block_region(0, 0);
    }
    else {
        // At least one bit is set so find_last_bit() should not return 'outer'.
        region.outer = find_last_bit(page_mask->bitmap, outer) + 1;
        UVM_ASSERT(region.outer <= outer);
    }

    return region;
}

static bool uvm_page_mask_test(const uvm_page_mask_t *mask, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < PAGES_PER_UVM_VA_BLOCK);

    return test_bit(page_index, mask->bitmap);
}

static bool uvm_page_mask_test_and_set(uvm_page_mask_t *mask, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < PAGES_PER_UVM_VA_BLOCK);

    return __test_and_set_bit(page_index, mask->bitmap);
}

static bool uvm_page_mask_test_and_clear(uvm_page_mask_t *mask, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < PAGES_PER_UVM_VA_BLOCK);

    return __test_and_clear_bit(page_index, mask->bitmap);
}

static void uvm_page_mask_set(uvm_page_mask_t *mask, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < PAGES_PER_UVM_VA_BLOCK);

    __set_bit(page_index, mask->bitmap);
}

static void uvm_page_mask_clear(uvm_page_mask_t *mask, uvm_page_index_t page_index)
{
    UVM_ASSERT(page_index < PAGES_PER_UVM_VA_BLOCK);

    __clear_bit(page_index, mask->bitmap);
}

static bool uvm_page_mask_region_test(const uvm_page_mask_t *mask,
                                      uvm_va_block_region_t region,
                                      uvm_page_index_t page_index)
{
    if (!uvm_va_block_region_contains_page(region, page_index))
        return false;

    return !mask || uvm_page_mask_test(mask, page_index);
}

static NvU32 uvm_page_mask_region_weight(const uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    NvU32 weight_before = 0;

    if (region.first > 0)
        weight_before = bitmap_weight(mask->bitmap, region.first);

    return bitmap_weight(mask->bitmap, region.outer) - weight_before;
}

static bool uvm_page_mask_region_empty(const uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    return find_next_bit(mask->bitmap, region.outer, region.first) == region.outer;
}

static bool uvm_page_mask_region_full(const uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    return find_next_zero_bit(mask->bitmap, region.outer, region.first) == region.outer;
}

static void uvm_page_mask_region_fill(uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    bitmap_set(mask->bitmap, region.first, region.outer - region.first);
}

static void uvm_page_mask_region_clear(uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    bitmap_clear(mask->bitmap, region.first, region.outer - region.first);
}

static void uvm_page_mask_region_clear_outside(uvm_page_mask_t *mask, uvm_va_block_region_t region)
{
    if (region.first > 0)
        bitmap_clear(mask->bitmap, 0, region.first);
    if (region.outer < PAGES_PER_UVM_VA_BLOCK)
        bitmap_clear(mask->bitmap, region.outer, PAGES_PER_UVM_VA_BLOCK - region.outer);
}

static void uvm_page_mask_zero(uvm_page_mask_t *mask)
{
    bitmap_zero(mask->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_empty(const uvm_page_mask_t *mask)
{
    return bitmap_empty(mask->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_full(const uvm_page_mask_t *mask)
{
    return bitmap_full(mask->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_and(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in1, const uvm_page_mask_t *mask_in2)
{
    return bitmap_and(mask_out->bitmap, mask_in1->bitmap, mask_in2->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_andnot(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in1, const uvm_page_mask_t *mask_in2)
{
    return bitmap_andnot(mask_out->bitmap, mask_in1->bitmap, mask_in2->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static void uvm_page_mask_or(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in1, const uvm_page_mask_t *mask_in2)
{
    bitmap_or(mask_out->bitmap, mask_in1->bitmap, mask_in2->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static void uvm_page_mask_complement(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in)
{
    bitmap_complement(mask_out->bitmap, mask_in->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static void uvm_page_mask_copy(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in)
{
    bitmap_copy(mask_out->bitmap, mask_in->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static NvU32 uvm_page_mask_weight(const uvm_page_mask_t *mask)
{
    return bitmap_weight(mask->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_subset(const uvm_page_mask_t *subset, const uvm_page_mask_t *mask)
{
    return bitmap_subset(subset->bitmap, mask->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_equal(const uvm_page_mask_t *mask_in1, const uvm_page_mask_t *mask_in2)
{
    return bitmap_equal(mask_in1->bitmap, mask_in2->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_init_from_region(uvm_page_mask_t *mask_out,
                                           uvm_va_block_region_t region,
                                           const uvm_page_mask_t *mask_in)
{
    uvm_page_mask_zero(mask_out);
    uvm_page_mask_region_fill(mask_out, region);

    if (mask_in)
        return uvm_page_mask_and(mask_out, mask_out, mask_in);

    return true;
}

static void uvm_page_mask_shift_right(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in, unsigned shift)
{
    bitmap_shift_right(mask_out->bitmap, mask_in->bitmap, shift, PAGES_PER_UVM_VA_BLOCK);
}

static void uvm_page_mask_shift_left(uvm_page_mask_t *mask_out, const uvm_page_mask_t *mask_in, unsigned shift)
{
    bitmap_shift_left(mask_out->bitmap, mask_in->bitmap, shift, PAGES_PER_UVM_VA_BLOCK);
}

static bool uvm_page_mask_intersects(const uvm_page_mask_t *mask1, const uvm_page_mask_t *mask2)
{
    return bitmap_intersects(mask1->bitmap, mask2->bitmap, PAGES_PER_UVM_VA_BLOCK);
}

// Print the given page mask on the given buffer using hex symbols. The
// minimum required size of the buffer is UVM_PAGE_MASK_PRINT_MIN_BUFFER_SIZE.
static void uvm_page_mask_print(const uvm_page_mask_t *mask, char *buffer)
{
    // There are two cases, which depend on PAGE_SIZE
    if (PAGES_PER_UVM_VA_BLOCK > 32) {
        NvLength current_long_idx = UVM_PAGE_MASK_WORDS - 1;
        const char *buffer_end = buffer + UVM_PAGE_MASK_PRINT_MIN_BUFFER_SIZE;

        UVM_ASSERT(sizeof(*mask->bitmap) == 8);

        // For 4KB pages, we need to iterate over multiple words
        do {
            NvU64 current_long = mask->bitmap[current_long_idx];

            buffer += sprintf(buffer, "%016llx", current_long);
            if (current_long_idx != 0)
                buffer += sprintf(buffer, ":");
        } while (current_long_idx-- != 0);

        UVM_ASSERT(buffer <= buffer_end);
    }
    else {
        NvU32 value = (unsigned)*mask->bitmap;

        UVM_ASSERT(PAGES_PER_UVM_VA_BLOCK == 32);

        // For 64KB pages, a single print suffices
        sprintf(buffer, "%08x", value);
    }
}

static uvm_va_block_region_t uvm_va_block_first_subregion_in_mask(uvm_va_block_region_t region,
                                                                  const uvm_page_mask_t *page_mask)
{
    uvm_va_block_region_t subregion;

    if (!page_mask)
        return region;

    subregion.first = find_next_bit(page_mask->bitmap, region.outer, region.first);
    subregion.outer = find_next_zero_bit(page_mask->bitmap, region.outer, subregion.first + 1);
    return subregion;
}

static uvm_va_block_region_t uvm_va_block_next_subregion_in_mask(uvm_va_block_region_t region,
                                                                 const uvm_page_mask_t *page_mask,
                                                                 uvm_va_block_region_t previous_subregion)
{
    uvm_va_block_region_t subregion;

    if (!page_mask) {
        subregion.first = region.outer;
        subregion.outer = region.outer;
        return subregion;
    }

    subregion.first = find_next_bit(page_mask->bitmap, region.outer, previous_subregion.outer + 1);
    subregion.outer = find_next_zero_bit(page_mask->bitmap, region.outer, subregion.first + 1);
    return subregion;
}

// Iterate over contiguous subregions of the region given by the page mask.
// If the page mask is NULL then it behaves as if it was a fully set mask and
// the only subregion iterated over will be the region itself.
#define for_each_va_block_subregion_in_mask(subregion, page_mask, region)                       \
    for ((subregion) = uvm_va_block_first_subregion_in_mask((region), (page_mask));             \
         (subregion).first != (region).outer;                                                   \
         (subregion) = uvm_va_block_next_subregion_in_mask((region), (page_mask), (subregion)))

static uvm_page_index_t uvm_va_block_first_page_in_mask(uvm_va_block_region_t region,
                                                        const uvm_page_mask_t *page_mask)
{
    if (page_mask)
        return find_next_bit(page_mask->bitmap, region.outer, region.first);
    else
        return region.first;
}

static uvm_page_index_t uvm_va_block_next_page_in_mask(uvm_va_block_region_t region,
                                                       const uvm_page_mask_t *page_mask,
                                                       uvm_page_index_t previous_page)
{
    if (page_mask) {
        return find_next_bit(page_mask->bitmap, region.outer, previous_page + 1);
    }
    else {
        UVM_ASSERT(previous_page < region.outer);
        return previous_page + 1;
    }
}

static uvm_page_index_t uvm_va_block_first_unset_page_in_mask(uvm_va_block_region_t region,
                                                              const uvm_page_mask_t *page_mask)
{
    if (page_mask)
        return find_next_zero_bit(page_mask->bitmap, region.outer, region.first);
    else
        return region.first;
}

static uvm_page_index_t uvm_va_block_next_unset_page_in_mask(uvm_va_block_region_t region,
                                                             const uvm_page_mask_t *page_mask,
                                                             uvm_page_index_t previous_page)
{
    if (page_mask) {
        return find_next_zero_bit(page_mask->bitmap, region.outer, previous_page + 1);
    }
    else {
        UVM_ASSERT(previous_page < region.outer);
        return previous_page + 1;
    }
}

static NvU64 uvm_reverse_map_start(const uvm_reverse_map_t *reverse_map)
{
    return uvm_va_block_cpu_page_address(reverse_map->va_block, reverse_map->region.first);
}

static NvU64 uvm_reverse_map_end(const uvm_reverse_map_t *reverse_map)
{
    return uvm_va_block_cpu_page_address(reverse_map->va_block, reverse_map->region.first) +
           uvm_va_block_region_size(reverse_map->region) - 1;
}

// Iterate over contiguous pages of the region given by the page mask.
// If the page mask is NULL then it behaves as if it was a fully set mask and
// it will iterate over all pages within the region.
#define for_each_va_block_page_in_region_mask(page_index, page_mask, region)                 \
    for ((page_index) = uvm_va_block_first_page_in_mask((region), (page_mask));              \
         (page_index) != (region).outer;                                                     \
         (page_index) = uvm_va_block_next_page_in_mask((region), (page_mask), (page_index)))

// Same as for_each_va_block_page_in_region_mask, but the region spans the
// whole given VA block
#define for_each_va_block_page_in_mask(page_index, page_mask, va_block)                      \
    for_each_va_block_page_in_region_mask(page_index, page_mask, uvm_va_block_region_from_block(va_block))

// Similar to for_each_va_block_page_in_region_mask, but iterating over pages
// whose bit is unset.
#define for_each_va_block_unset_page_in_region_mask(page_index, page_mask, region)           \
    for ((page_index) = uvm_va_block_first_unset_page_in_mask((region), (page_mask));        \
         (page_index) != (region).outer;                                                     \
         (page_index) = uvm_va_block_next_unset_page_in_mask((region), (page_mask), (page_index)))

// Similar to for_each_va_block_page_in_mask, but iterating over pages whose
// bit is unset.
#define for_each_va_block_unset_page_in_mask(page_index, page_mask, va_block)                \
    for_each_va_block_unset_page_in_region_mask(page_index, page_mask, uvm_va_block_region_from_block(va_block))

// Iterate over all pages within the given region
#define for_each_va_block_page_in_region(page_index, region)                                 \
    for_each_va_block_page_in_region_mask((page_index), NULL, (region))

// Iterate over all pages within the given VA block
#define for_each_va_block_page(page_index, va_block)                                         \
    for_each_va_block_page_in_region((page_index), uvm_va_block_region_from_block(va_block))

// Return the first vma intersecting the region [start, va_block->end]
// or NULL if no such vma exists. Also returns the region covered by
// the vma within the va_block.
struct vm_area_struct *uvm_va_block_find_vma_region(uvm_va_block_t *va_block,
                                                    struct mm_struct *mm,
                                                    NvU64 start,
                                                    uvm_va_block_region_t *region);

// Iterate over all vma regions covered by a va_block
#define for_each_va_block_vma_region(va_block, mm, vma, region)                                 \
    for (vma = uvm_va_block_find_vma_region((va_block), (mm), (va_block)->start, (region));     \
         (vma);                                                                                 \
         vma = uvm_va_block_find_vma_region((va_block),                                         \
                                            (mm),                                               \
                                            uvm_va_block_region_end((va_block), *(region)) + 1, \
                                            (region)))

// Return the block region covered by the given chunk size. page_index must be
// any page within the block known to be covered by the chunk.
static uvm_va_block_region_t uvm_va_block_chunk_region(uvm_va_block_t *block,
                                                       uvm_chunk_size_t chunk_size,
                                                       uvm_page_index_t page_index)
{
    NvU64 page_addr = uvm_va_block_cpu_page_address(block, page_index);
    NvU64 chunk_start_addr = UVM_ALIGN_DOWN(page_addr, chunk_size);
    uvm_page_index_t first = (uvm_page_index_t)((chunk_start_addr - block->start) / PAGE_SIZE);
    return uvm_va_block_region(first, first + (chunk_size / PAGE_SIZE));
}

//
// Helpers for page state (permissions, size, residency)
//

bool uvm_va_block_page_is_gpu_authorized(uvm_va_block_t *va_block,
                                         uvm_page_index_t page_index,
                                         uvm_gpu_id_t gpu_id,
                                         uvm_prot_t required_prot);

// Compute the processors that have a copy of the given page resident in their
// memory.
void uvm_va_block_page_resident_processors(uvm_va_block_t *va_block,
                                           uvm_page_index_t page_index,
                                           uvm_processor_mask_t *resident_processors);

// Count how many processors have a copy of the given page resident in their
// memory.
NvU32 uvm_va_block_page_resident_processors_count(uvm_va_block_t *va_block, uvm_page_index_t page_index);

// Get the processor with a resident copy of a page closest to the given
// processor.
uvm_processor_id_t uvm_va_block_page_get_closest_resident(uvm_va_block_t *va_block,
                                                          uvm_page_index_t page_index,
                                                          uvm_processor_id_t processor);

// Insert a CPU chunk at the given page_index into the va_block.
// Locking: The va_block lock must be held.
NV_STATUS uvm_cpu_chunk_insert_in_block(uvm_va_block_t *va_block,
                                        uvm_cpu_chunk_t *chunk,
                                        uvm_page_index_t page_index);

// Remove a CPU chunk at the given page_index from the va_block.
// Locking: The va_block lock must be held.
void uvm_cpu_chunk_remove_from_block(uvm_va_block_t *va_block,
                                     uvm_page_index_t page_index);

// Return the CPU chunk at the given page_index from the va_block.
// Locking: The va_block lock must be held.
uvm_cpu_chunk_t *uvm_cpu_chunk_get_chunk_for_page(uvm_va_block_t *va_block,
                                                  uvm_page_index_t page_index);

// Return the CPU chunk at the given page_index from the va_block.
// Locking: The va_block lock must be held.
struct page *uvm_cpu_chunk_get_cpu_page(uvm_va_block_t *va_block,
                                        uvm_page_index_t page_index);

// Physically map a CPU chunk so it is DMA'able from all registered GPUs.
// Locking: The va_block lock must be held.
NV_STATUS uvm_va_block_map_cpu_chunk_on_gpus(uvm_va_block_t *va_block,
                                             uvm_page_index_t page_index);

// Physically unmap a CPU chunk from all registered GPUs.
// Locking: The va_block lock must be held.
void uvm_va_block_unmap_cpu_chunk_on_gpus(uvm_va_block_t *va_block,
                                          uvm_cpu_chunk_t *chunk,
                                          uvm_page_index_t page_index);

// Remove any CPU chunks in the given region.
// Locking: The va_block lock must be held.
void uvm_va_block_remove_cpu_chunks(uvm_va_block_t *va_block, uvm_va_block_region_t region);

// Get CPU page size or 0 if it is not mapped
NvU32 uvm_va_block_page_size_cpu(uvm_va_block_t *va_block,
                                 uvm_page_index_t page_index);

// Get GPU page size or 0 if it is not mapped on the given GPU
NvU32 uvm_va_block_page_size_gpu(uvm_va_block_t *va_block, uvm_gpu_id_t gpu_id, uvm_page_index_t page_index);

// Get page size or 0 if it is not mapped on the given processor
static NvU32 uvm_va_block_page_size_processor(uvm_va_block_t *va_block,
                                              uvm_processor_id_t processor_id,
                                              uvm_page_index_t page_index)
{
    if (UVM_ID_IS_CPU(processor_id))
        return uvm_va_block_page_size_cpu(va_block, page_index);
    else
        return uvm_va_block_page_size_gpu(va_block, processor_id, page_index);
}

// Returns the big page size for the GPU VA space of the block
NvU32 uvm_va_block_gpu_big_page_size(uvm_va_block_t *va_block, uvm_gpu_t *gpu);

// Returns the number of big pages in the VA block for the given size
size_t uvm_va_block_num_big_pages(uvm_va_block_t *va_block, NvU32 big_page_size);

// Returns the number of big pages in the VA block for the big page size on the
// given GPU
static size_t uvm_va_block_gpu_num_big_pages(uvm_va_block_t *va_block, uvm_gpu_t *gpu)
{
    return uvm_va_block_num_big_pages(va_block, uvm_va_block_gpu_big_page_size(va_block, gpu));
}

// Returns the start address of the given big page index and big page size
NvU64 uvm_va_block_big_page_addr(uvm_va_block_t *va_block, size_t big_page_index, NvU32 big_page_size);

// Returns the region [start, end] of the given big page index and big page size
uvm_va_block_region_t uvm_va_block_big_page_region(uvm_va_block_t *va_block,
                                                   size_t big_page_index,
                                                   NvU32 big_page_size);

// Returns the largest sub-region region of [start, end] which can fit big
// pages. If the region cannot fit any big pages, an invalid region (0, 0) is
// returned.
uvm_va_block_region_t uvm_va_block_big_page_region_all(uvm_va_block_t *va_block, NvU32 big_page_size);

// Returns the largest sub-region region of 'region' which can fit big pages.
// If the region cannot fit any big pages, an invalid region (0, 0) is returned.
uvm_va_block_region_t uvm_va_block_big_page_region_subset(uvm_va_block_t *va_block,
                                                          uvm_va_block_region_t region,
                                                          NvU32 big_page_size);

// Returns the big page index (the bit index within
// uvm_va_block_gpu_state_t::big_ptes) corresponding to page_index. If
// page_index cannot be covered by a big PTE due to alignment or block size,
// MAX_BIG_PAGES_PER_UVM_VA_BLOCK is returned.
size_t uvm_va_block_big_page_index(uvm_va_block_t *va_block, uvm_page_index_t page_index, NvU32 big_page_size);

// Returns the new residency for a page that faulted or triggered access
// counter notifications. The read_duplicate output parameter indicates if the
// page meets the requirements to be read-duplicated
// va_block_context must not be NULL, va_block_context->policy must be valid,
// and if the va_block is a HMM block, va_block_context->hmm.vma must be valid
// which also means the va_block_context->mm is not NULL, retained, and locked
// for at least read. See the comments for uvm_va_block_check_policy_is_valid()
// and uvm_hmm_check_context_vma_is_valid() in uvm_hmm.h.
// Locking: the va_block lock must be held.
uvm_processor_id_t uvm_va_block_select_residency(uvm_va_block_t *va_block,
                                                 uvm_va_block_context_t *va_block_context,
                                                 uvm_page_index_t page_index,
                                                 uvm_processor_id_t processor_id,
                                                 NvU32 access_type_mask,
                                                 const uvm_va_policy_t *policy,
                                                 const uvm_perf_thrashing_hint_t *thrashing_hint,
                                                 uvm_service_operation_t operation,
                                                 bool *read_duplicate);

// Return the maximum mapping protection for processor_id that will not require
// any permision revocation on the rest of processors.
uvm_prot_t uvm_va_block_page_compute_highest_permission(uvm_va_block_t *va_block,
                                                        uvm_processor_id_t processor_id,
                                                        uvm_page_index_t page_index);

// A helper macro for handling allocation-retry
//
// The macro takes a VA block, uvm_va_block_retry_t struct and a function call
// to retry as long as it returns NV_ERR_MORE_PROCESSING_REQUIRED.
//
// block_retry can be NULL if it's not necessary for the function call,
// otherwise it will be initialized and deinitialized by the macro.
//
// The macro also locks and unlocks the block's lock internally as it's expected
// that the block's lock has been unlocked and relocked whenever the function call
// returns NV_ERR_MORE_PROCESSING_REQUIRED and this makes it clear that the
// block's state is not locked across these calls.
#define UVM_VA_BLOCK_LOCK_RETRY(va_block, block_retry, call) ({     \
    NV_STATUS status;                                               \
    uvm_va_block_t *__block = (va_block);                           \
    uvm_va_block_retry_t *__retry = (block_retry);                  \
                                                                    \
    uvm_va_block_retry_init(__retry);                               \
                                                                    \
    uvm_mutex_lock(&__block->lock);                                 \
                                                                    \
    do {                                                            \
        status = (call);                                            \
    } while (status == NV_ERR_MORE_PROCESSING_REQUIRED);            \
                                                                    \
    uvm_mutex_unlock(&__block->lock);                               \
                                                                    \
    uvm_va_block_retry_deinit(__retry, __block);                    \
                                                                    \
    status;                                                         \
})

// A helper macro for handling allocation-retry
//
// The macro takes a VA block, uvm_va_block_retry_t struct and a function call
// to retry as long as it returns NV_ERR_MORE_PROCESSING_REQUIRED.
//
// block_retry can be NULL if it's not necessary for the function call,
// otherwise it will be initialized and deinitialized by the macro.
//
// This macro, as opposed to UVM_VA_BLOCK_LOCK_RETRY(), expects the block lock
// to be already taken. Notably the block's lock might be unlocked and relocked
// as part of the call.
#define UVM_VA_BLOCK_RETRY_LOCKED(va_block, block_retry, call) ({   \
    NV_STATUS status;                                               \
    uvm_va_block_t *__block = (va_block);                           \
    uvm_va_block_retry_t *__retry = (block_retry);                  \
                                                                    \
    uvm_va_block_retry_init(__retry);                               \
                                                                    \
    uvm_assert_mutex_locked(&__block->lock);                        \
                                                                    \
    do {                                                            \
        status = (call);                                            \
    } while (status == NV_ERR_MORE_PROCESSING_REQUIRED);            \
                                                                    \
    uvm_va_block_retry_deinit(__retry, __block);                    \
                                                                    \
    status;                                                         \
})

#endif // __UVM_VA_BLOCK_H__