/*******************************************************************************
    Copyright (c) 2018-2025 NVIDIA Corporation

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    of this software and associated documentation files (the "Software"), to
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    rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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        The above copyright notice and this permission notice shall be
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    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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*******************************************************************************/

#include "uvm_common.h"
#include "uvm_kvmalloc.h"
#include "uvm_va_space.h"
#include "uvm_va_space_mm.h"
#include "uvm_ats.h"
#include "uvm_api.h"
#include "uvm_test.h"
#include "uvm_test_ioctl.h"

//
// This comment block describes some implementation rationale. See the header
// for the API descriptions.
//
// ========================= Retain count vs mm_users ==========================
//
// To guarantee the mm is available and won't be destroyed we require
// userspace to open a second file descriptor (uvm_mm_fd) and
// initialize it with uvm_api_mm_initialize(). During initialization
// we take a mm_users reference to ensure the mm remains valid until
// the file descriptor is closed.
//
// To ensure userspace can't close the file descriptor and drop the
// mm_users refcount while it is in use threads must call either
// uvm_va_space_mm_retain() or uvm_va_space_mm_or_current_retain() to
// increment the retained count. This also checks that userspace has
// initialized the uvm_mm_fd and therefore holds a valid pagetable
// pin.
//
// Closing uvm_mm_fd will call uvm_va_space_mm_shutdown() prior to
// mmput() which ensures there are no active users of the mm. This
// indirection is required because not all threads can call mmput()
// directly. In particular the replayable GPU fault handling path
// can't call mmput() because it may result in exit_mmap() which could
// result in RM calls and VA space destroy and those need to wait for
// the GPU fault handler to finish.
//
// ============================ Handling mm teardown ===========================
//
// When the process is exiting we will get notified either via an
// explict close of uvm_mm_fd or implicitly as part of
// exit_files(). We are guaranteed to get this call because we don't
// allow mmap on uvm_mm_fd, and the userspace pagetables (mm_users)
// are guaranteed to exist because we hold a mm_users refcount
// which is released as part of file close.
//
// This allows any outstanding GPU faults to be processed. To prevent
// new faults occurring uvm_va_space_mm_shutdown() is called to stop
// all GPU memory accesses to the mm. Once all GPU memory has been
// stopped no new retainers of the va_space will be allowed and the
// mm_users reference will be dropped, potentially tearing down the mm
// and associated pagetables.
//
// This essentially shuts down the VA space for new work. The VA space
// object remains valid for most teardown ioctls until the file is
// closed, because it's legal for the associated process to die then
// for another process with a reference on the file to perform the
// unregisters or associated ioctls.  This is particularly true for
// tools users.
//
// An exception to the above is UvmUnregisterChannel. Since channels are
// completely removed from the VA space on mm teardown, later channel
// unregisters will fail to find the handles and will return an error.
//
// At a high level, the sequence of operations to perform prior to mm
// teardown is:
//
// 1) Stop all channels
//      - Prevents new faults and accesses on non-MPS
// 2) Detach all channels
//      - Prevents pending faults from being translated to this VA space
//      - Non-replayable faults will be dropped so no new ones can arrive
//      - Access counter notifications will be prevented from getting new
//        translations to this VA space. Pending entries may attempt to retain
//        the mm, but will drop the notification if they can't be serviced.
// 3) Flush the fault buffer
//      - The only reason to flush the fault buffer is to avoid spurious
//        cancels. If we didn't flush the fault buffer before marking the mm
//        as dead, then remaining faults which require the mm would be
//        cancelled. Since the faults might be stale, we would record cancel
//        events which didn't really happen (the access didn't happen after
//        the mm died). By flushing we clear out all stale faults, and in
//        the case of MPS, cancel real faults after.
// 4) UnsetPageDir
//      - Prevents new accesses on MPS
// 5) Mark the va_space_mm as released
//      - Prevents new retainers from using the mm. There won't be any more on
//        the fault handling paths, but there could be others in worker threads.
//
// Here are some tables of each step in the sequence, and what operations can
// still be performed after each step. This is all from the perspective of a
// single VA space. "Untranslated" means that the fault entry has not been
// translated to a uvm_va_space yet.
//
// Replayable non-MPS Behavior:
//
//                  Can              Pending         Pending         Can be
//                  access   Can     untranslated    translated      servicing
//                  memory   fault   faults          faults          faults
// -----------------------------------------------------------------------------
// Shutdown start   Yes      Yes     Service         Service         Yes
// Stop channels    No       No      Service [1]     Service [1]     Yes [1]
// Detach channels  No       No      Flush buffer    Service [1]     Yes [1], [2]
// Flush buffer     No       No      None possible   None possible   No
// UnsetPageDir     No       No      None possible   None possible   No
//
//
// Replayable MPS Behavior:
//
//                  Can              Pending         Pending         Can be
//                  access   Can     untranslated    translated      servicing
//                  memory   fault   faults          faults          faults
// -----------------------------------------------------------------------------
// Shutdown start   Yes      Yes     Service         Service         Yes
// Stop channels    Yes      Yes     Service         Service         Yes
// Detach channels  Yes      Yes     Cancel, flush   Service         Yes
// Flush buffer     Yes      Yes     Cancel, flush   None possible   No
// UnsetPageDir     No [3]   Yes     Cancel, flush   None possible   No
//
//
// [1]: All pending faults in this VA space are stale since channel stop
//      preempted the context.
// [2]: Faults in this VA space can't be serviced concurrently with detach since
//      detach holds the VA space lock in write mode. Faults in other VA spaces
//      can be serviced, and stale faults in this VA space can resume service
//      after detach is done.
// [3]: Due to the nature of MPS, remaining work which had started under the VA
//      space could still execute and attempt to make memory accesses. However,
//      since the PDB at that point is empty and ATS is disabled (if available),
//      all accesses will fault and be cancelled rather than successfully
//      translate to physical memory.
//
// =============================================================================

static void uvm_va_space_mm_shutdown(uvm_va_space_t *va_space);

static int uvm_enable_va_space_mm = 1;
module_param(uvm_enable_va_space_mm, int, S_IRUGO);
MODULE_PARM_DESC(uvm_enable_va_space_mm,
                 "Set to 0 to disable UVM from using mmu_notifiers to create "
                 "an association between a UVM VA space and a process. This "
                 "will also disable pageable memory access via either ATS or "
                 "HMM.");

bool uvm_va_space_mm_enabled_system(void)
{
    return UVM_CAN_USE_MMU_NOTIFIERS() && uvm_enable_va_space_mm;
}

bool uvm_va_space_mm_enabled(uvm_va_space_t *va_space)
{
    // A va_space doesn't have any association with an mm in multi-process
    // sharing mode.
    if (va_space->initialization_flags & UVM_INIT_FLAGS_MULTI_PROCESS_SHARING_MODE)
        return false;

    return uvm_va_space_mm_enabled_system();
}

NV_STATUS uvm_va_space_mm_register(uvm_va_space_t *va_space)
{
    uvm_va_space_mm_t *va_space_mm = &va_space->va_space_mm;

    uvm_assert_mmap_lock_locked_write(current->mm);
    uvm_assert_rwsem_locked_write(&va_space->lock);

    va_space_mm->state = UVM_VA_SPACE_MM_STATE_UNINITIALIZED;

    if (!uvm_va_space_mm_enabled(va_space))
        return NV_OK;

    UVM_ASSERT(!va_space_mm->mm);
    va_space_mm->mm = current->mm;
    uvm_mmgrab(va_space_mm->mm);

    if ((UVM_IS_CONFIG_HMM() || UVM_HMM_RANGE_FAULT_SUPPORTED()) &&
        uvm_va_space_pageable_mem_access_supported(va_space)) {

        #if UVM_CAN_USE_MMU_NOTIFIERS()
            int ret;

            // Initialize MMU interval notifiers for this process. This allows
            // mmu_interval_notifier_insert() to be called without holding the
            // mmap_lock for write.
            // Note: there is no __mmu_notifier_unregister(), this call just
            // allocates memory which is attached to the mm_struct and freed
            // when the mm_struct is freed.
            ret = __mmu_notifier_register(NULL, current->mm);
            if (ret)
                return errno_to_nv_status(ret);
        #else
            UVM_ASSERT(0);
        #endif
    }

    return NV_OK;
}

void uvm_va_space_mm_unregister(uvm_va_space_t *va_space)
{
    uvm_va_space_mm_t *va_space_mm = &va_space->va_space_mm;

    // We can't hold the VA space lock or mmap_lock because
    // uvm_va_space_mm_shutdown() waits for retainers which may take
    // these locks.
    uvm_assert_unlocked_order(UVM_LOCK_ORDER_MMAP_LOCK);
    uvm_assert_unlocked_order(UVM_LOCK_ORDER_VA_SPACE);

    uvm_va_space_mm_shutdown(va_space);
    UVM_ASSERT(va_space_mm->retained_count == 0);

    // Only happens if uvm_va_space_mm_register() fails
    if (!va_space_mm->mm)
        return;

    if (uvm_va_space_mm_enabled(va_space))
        uvm_mmdrop(va_space_mm->mm);
}

struct mm_struct *uvm_va_space_mm_retain(uvm_va_space_t *va_space)
{
    uvm_va_space_mm_t *va_space_mm = &va_space->va_space_mm;
    struct mm_struct *mm = NULL;

    if (!uvm_va_space_mm_enabled(va_space))
        return NULL;

    uvm_spin_lock(&va_space_mm->lock);

    if (!uvm_va_space_mm_alive(va_space_mm))
        goto out;

    ++va_space_mm->retained_count;

    mm = va_space_mm->mm;
    UVM_ASSERT(mm);

out:

    // uvm_api_mm_init() holds a reference
    if (mm)
        UVM_ASSERT(atomic_read(&mm->mm_users) > 0);

    uvm_spin_unlock(&va_space_mm->lock);

    return mm;
}

struct mm_struct *uvm_va_space_mm_or_current_retain(uvm_va_space_t *va_space)
{
    // We should only attempt to use current->mm from a user thread
    UVM_ASSERT(!(current->flags & PF_KTHREAD));

    // current->mm is NULL when we're in process teardown. In that case it
    // doesn't make sense to use any mm.
    if (!current->mm)
        return NULL;

    // If !uvm_va_space_mm_enabled() we use current->mm on the ioctl
    // paths. In that case we don't need to mmget(current->mm) because
    // the current thread mm is always valid. On
    // uvm_va_space_mm_enabled() systems we skip trying to retain the
    // mm if it is current->mm because userspace may not have
    // initialised the mm fd but UVM callers on the ioctl path still
    // assume retaining current->mm will succeed.
    if (!uvm_va_space_mm_enabled(va_space))
        return current->mm;

    return uvm_va_space_mm_retain(va_space);
}

void uvm_va_space_mm_release(uvm_va_space_t *va_space)
{
    uvm_va_space_mm_t *va_space_mm = &va_space->va_space_mm;

    UVM_ASSERT(uvm_va_space_mm_enabled(va_space));

    // The mm must not have been torn down while we have it retained
    UVM_ASSERT(va_space_mm->mm);

    uvm_spin_lock(&va_space_mm->lock);

    UVM_ASSERT(va_space_mm->retained_count > 0);
    --va_space_mm->retained_count;

    // If we're the last retainer on a dead mm, signal any potential waiters
    if (va_space_mm->retained_count == 0 && !uvm_va_space_mm_alive(va_space_mm)) {
        uvm_spin_unlock(&va_space_mm->lock);

        // There could be a thread in uvm_va_space_mm_shutdown()
        // waiting on us, so wake it up.
        wake_up(&va_space_mm->last_retainer_wait_queue);
    }
    else {
        uvm_spin_unlock(&va_space_mm->lock);
    }
}

void uvm_va_space_mm_or_current_release(uvm_va_space_t *va_space, struct mm_struct *mm)
{
    if (!uvm_va_space_mm_enabled(va_space) || !mm)
        return;

    uvm_va_space_mm_release(va_space);
}

static void uvm_va_space_mm_shutdown(uvm_va_space_t *va_space)
{
    uvm_va_space_mm_t *va_space_mm = &va_space->va_space_mm;
    uvm_gpu_va_space_t *gpu_va_space;
    uvm_gpu_t *gpu;
    uvm_processor_mask_t *retained_gpus = &va_space_mm->scratch_processor_mask;
    uvm_parent_processor_mask_t flushed_parent_gpus;
    LIST_HEAD(deferred_free_list);

    uvm_va_space_down_write(va_space);

    // Prevent future registrations of any kind. We'll be iterating over all
    // GPUs and GPU VA spaces below but taking and dropping the VA space lock.
    // It's ok for other threads to unregister those objects, but not to
    // register new ones.
    //
    // We also need to prevent new channel work from arriving since we're trying
    // to stop memory accesses.
    va_space->disallow_new_registers = true;

    uvm_va_space_downgrade_write_rm(va_space);

    // Stop channels to prevent new accesses and new faults on non-MPS
    uvm_va_space_stop_all_user_channels(va_space);

    uvm_va_space_up_read_rm(va_space);

    // Detach all channels to prevent pending untranslated faults from getting
    // to this VA space. This also removes those channels from the VA space and
    // puts them on the deferred free list.
    uvm_va_space_down_write(va_space);
    uvm_va_space_detach_all_user_channels(va_space, &deferred_free_list);
    uvm_processor_mask_copy(retained_gpus, &va_space->registered_gpus);
    uvm_global_gpu_retain(retained_gpus);
    uvm_va_space_up_write(va_space);

    // It's ok to use retained_gpus outside the lock since there can only be one
    // thread executing in uvm_va_space_mm_shutdown at a time.

    // Flush the replayable fault buffer on all registered faultable GPUs.
    // This will avoid spurious cancels of stale pending translated
    // faults after we set UVM_VA_SPACE_MM_STATE_RELEASED later. This is
    // unnecessary for non-replayable faults because that handler ignores faults
    // if the channel has been destroyed, before the mm is checked.
    uvm_parent_processor_mask_zero(&flushed_parent_gpus);
    for_each_gpu_in_mask(gpu, retained_gpus) {
        if (!uvm_parent_processor_mask_test_and_set(&flushed_parent_gpus, gpu->parent->id))
            uvm_gpu_replayable_buffer_flush(gpu);
    }

    uvm_global_gpu_release(retained_gpus);

    // Call nvUvmInterfaceUnsetPageDirectory. This has no effect on non-MPS.
    // Under MPS this guarantees that no new GPU accesses will be made using
    // this mm.
    //
    // We need only one thread to make this call, but we could have one thread
    // in here and one in destroy_gpu_va_space. Serialize these by starting in
    // write mode then downgrading to read.
    uvm_va_space_down_write(va_space);
    uvm_va_space_downgrade_write_rm(va_space);
    for_each_gpu_va_space(gpu_va_space, va_space)
        uvm_gpu_va_space_unset_page_dir(gpu_va_space);
    uvm_va_space_up_read_rm(va_space);

    // The above call to uvm_gpu_va_space_unset_page_dir handles the GPU VA
    // spaces which are known to be registered. However, we could've raced with
    // a concurrent uvm_va_space_unregister_gpu_va_space, giving this sequence:
    //
    // unregister_gpu_va_space                  uvm_va_space_mm_shutdown
    //     uvm_va_space_down_write
    //     remove_gpu_va_space
    //     uvm_va_space_up_write
    //                                          uvm_va_space_down_write(va_space);
    //                                          // No GPU VA spaces
    //                                          Unlock, return
    //     uvm_deferred_free_object_list
    //         uvm_gpu_va_space_unset_page_dir
    //
    // We have to be sure that all accesses in this GPU VA space are done before
    // returning, so we have to wait for the other thread to finish its
    // uvm_gpu_va_space_unset_page_dir call.
    //
    // We can be sure that num_pending will eventually go to zero because we've
    // prevented new GPU VA spaces from being registered above.
    wait_event(va_space->gpu_va_space_deferred_free.wait_queue,
               atomic_read(&va_space->gpu_va_space_deferred_free.num_pending) == 0);

    // Now that there won't be any new GPU faults, prevent subsequent retainers
    // from accessing this mm.
    uvm_spin_lock(&va_space_mm->lock);
    va_space_mm->state = UVM_VA_SPACE_MM_STATE_RELEASED;
    uvm_spin_unlock(&va_space_mm->lock);

    // Finish channel destroy. This can be done at any point after detach as
    // long as we don't hold the VA space lock.
    uvm_deferred_free_object_list(&deferred_free_list);

    // Flush out all pending retainers
    wait_event(va_space_mm->last_retainer_wait_queue, va_space_mm->retained_count == 0);
}

static NV_STATUS mm_read64(struct mm_struct *mm, NvU64 addr, NvU64 *val)
{
    long ret;
    struct page *page;
    NvU64 *mapping;

    UVM_ASSERT(IS_ALIGNED(addr, sizeof(*val)));

    uvm_down_read_mmap_lock(mm);
    ret = NV_PIN_USER_PAGES_REMOTE(mm, (unsigned long)addr, 1, 0, &page, NULL);
    uvm_up_read_mmap_lock(mm);

    if (ret < 0)
        return errno_to_nv_status(ret);

    UVM_ASSERT(ret == 1);

    mapping = (NvU64 *)((char *)kmap(page) + (addr % PAGE_SIZE));
    *val = *mapping;
    kunmap(page);
    NV_UNPIN_USER_PAGE(page);

    return NV_OK;
}

NV_STATUS uvm_test_va_space_mm_retain(UVM_TEST_VA_SPACE_MM_RETAIN_PARAMS *params, struct file *filp)
{
    uvm_va_space_t *va_space = NULL;
    struct mm_struct *mm = NULL;
    NV_STATUS status = NV_OK;

    if (!IS_ALIGNED(params->addr, sizeof(params->val_before)))
        return NV_ERR_INVALID_ARGUMENT;

    uvm_mutex_lock(&g_uvm_global.va_spaces.lock);

    list_for_each_entry(va_space, &g_uvm_global.va_spaces.list, list_node) {
        if ((uintptr_t)va_space == params->va_space_ptr) {
            mm = uvm_va_space_mm_retain(va_space);
            break;
        }
    }

    uvm_mutex_unlock(&g_uvm_global.va_spaces.lock);

    if ((uintptr_t)va_space != params->va_space_ptr)
        return NV_ERR_MISSING_TABLE_ENTRY;

    if (!mm)
        return NV_ERR_PAGE_TABLE_NOT_AVAIL;

    status = mm_read64(mm, params->addr, &params->val_before);

    if (status == NV_OK && params->sleep_us) {
        usleep_range(params->sleep_us, params->sleep_us + 1000);
        status = mm_read64(mm, params->addr, &params->val_after);
    }

    uvm_va_space_mm_release(va_space);
    return status;
}

NV_STATUS uvm_test_va_space_mm_or_current_retain(UVM_TEST_VA_SPACE_MM_OR_CURRENT_RETAIN_PARAMS *params,
                                                 struct file *filp)
{
    uvm_va_space_t *va_space = uvm_va_space_get(filp);
    struct mm_struct *mm;
    NV_STATUS status = NV_OK;

    mm = uvm_va_space_mm_or_current_retain(va_space);
    if (!mm)
        return NV_ERR_PAGE_TABLE_NOT_AVAIL;

    if (params->retain_done_ptr) {
        NvU64 flag = true;

        if (copy_to_user((void __user *)params->retain_done_ptr, &flag, sizeof(flag)))
            status = NV_ERR_INVALID_ARGUMENT;
    }

    if (status == NV_OK && params->sleep_us)
            usleep_range(params->sleep_us, params->sleep_us + 1000);

    uvm_va_space_mm_or_current_release(va_space, mm);

    return status;
}
