[PATCH] drm/amdgpu: Unlocked unmap only clear page table leaves
Christian König
christian.koenig at amd.com
Wed Jan 15 11:01:22 UTC 2025
Am 14.01.25 um 15:53 schrieb Philip Yang:
> SVM migration unmap pages from GPU and then update mapping to GPU to
> recover page fault. Currently unmap clears the PDE entry for range
> length >= huge page and free PTB bo, update mapping to alloc new PT bo.
> There is race bug that the freed entry bo maybe still on the pt_free
> list, reused when updating mapping and then freed, leave invalid PDE
> entry and cause GPU page fault.
>
> By setting the update to clear only one PDE entry or clear PTB, to
> avoid unmap to free PTE bo. This fixes the race bug and improve the
> unmap and map to GPU performance. Update mapping to huge page will
> still free the PTB bo.
>
> With this change, the vm->pt_freed list and work is not needed. Add
> WARN_ON(unlocked) in amdgpu_vm_pt_free_dfs to catch if unmap to free the
> PTB.
>
> Signed-off-by: Philip Yang <Philip.Yang at amd.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 4 ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 4 ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 43 +++++++----------------
> 3 files changed, 13 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index c9c48b782ec1..48b2c0b3b315 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -2440,8 +2440,6 @@ int amdgpu_vm_init(struct amdgpu_device *adev, struct amdgpu_vm *vm,
> spin_lock_init(&vm->status_lock);
> INIT_LIST_HEAD(&vm->freed);
> INIT_LIST_HEAD(&vm->done);
> - INIT_LIST_HEAD(&vm->pt_freed);
> - INIT_WORK(&vm->pt_free_work, amdgpu_vm_pt_free_work);
> INIT_KFIFO(vm->faults);
>
> r = amdgpu_vm_init_entities(adev, vm);
> @@ -2613,8 +2611,6 @@ void amdgpu_vm_fini(struct amdgpu_device *adev, struct amdgpu_vm *vm)
>
> amdgpu_amdkfd_gpuvm_destroy_cb(adev, vm);
>
> - flush_work(&vm->pt_free_work);
> -
> root = amdgpu_bo_ref(vm->root.bo);
> amdgpu_bo_reserve(root, true);
> amdgpu_vm_put_task_info(vm->task_info);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> index 5d119ac26c4f..160889e5e64d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> @@ -369,10 +369,6 @@ struct amdgpu_vm {
> /* BOs which are invalidated, has been updated in the PTs */
> struct list_head done;
>
> - /* PT BOs scheduled to free and fill with zero if vm_resv is not hold */
> - struct list_head pt_freed;
> - struct work_struct pt_free_work;
> -
> /* contains the page directory */
> struct amdgpu_vm_bo_base root;
> struct dma_fence *last_update;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> index f78a0434a48f..54ae0e9bc6d7 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> @@ -546,27 +546,6 @@ static void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry)
> amdgpu_bo_unref(&entry->bo);
> }
>
> -void amdgpu_vm_pt_free_work(struct work_struct *work)
> -{
> - struct amdgpu_vm_bo_base *entry, *next;
> - struct amdgpu_vm *vm;
> - LIST_HEAD(pt_freed);
> -
> - vm = container_of(work, struct amdgpu_vm, pt_free_work);
> -
> - spin_lock(&vm->status_lock);
> - list_splice_init(&vm->pt_freed, &pt_freed);
> - spin_unlock(&vm->status_lock);
> -
> - /* flush_work in amdgpu_vm_fini ensure vm->root.bo is valid. */
> - amdgpu_bo_reserve(vm->root.bo, true);
> -
> - list_for_each_entry_safe(entry, next, &pt_freed, vm_status)
> - amdgpu_vm_pt_free(entry);
> -
> - amdgpu_bo_unreserve(vm->root.bo);
> -}
> -
> /**
> * amdgpu_vm_pt_free_list - free PD/PT levels
> *
> @@ -579,19 +558,15 @@ void amdgpu_vm_pt_free_list(struct amdgpu_device *adev,
> struct amdgpu_vm_update_params *params)
> {
> struct amdgpu_vm_bo_base *entry, *next;
> - struct amdgpu_vm *vm = params->vm;
> bool unlocked = params->unlocked;
>
> if (list_empty(¶ms->tlb_flush_waitlist))
> return;
>
> - if (unlocked) {
> - spin_lock(&vm->status_lock);
> - list_splice_init(¶ms->tlb_flush_waitlist, &vm->pt_freed);
> - spin_unlock(&vm->status_lock);
> - schedule_work(&vm->pt_free_work);
> - return;
> - }
> + /*
> + * unlocked unmap clear page table leaves, warning to free the page entry.
> + */
> + WARN_ON(unlocked);
>
> list_for_each_entry_safe(entry, next, ¶ms->tlb_flush_waitlist, vm_status)
> amdgpu_vm_pt_free(entry);
> @@ -899,7 +874,15 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
> incr = (uint64_t)AMDGPU_GPU_PAGE_SIZE << shift;
> mask = amdgpu_vm_pt_entries_mask(adev, cursor.level);
> pe_start = ((cursor.pfn >> shift) & mask) * 8;
> - entry_end = ((uint64_t)mask + 1) << shift;
> +
> + if (cursor.level < AMDGPU_VM_PTB && params->unlocked)
> + /*
> + * MMU notifier callback unlocked unmap huge page, leave is PDE entry,
> + * only clear one entry. Next entry search again for PDE or PTE leave.
> + */
> + entry_end = 1ULL << shift;
> + else
> + entry_end = ((uint64_t)mask + 1) << shift;
That here looks to much like a hack for my taste. entry_end basically
denotes the end of the pages tables and not the updated region.
We already set frag_end to this here:
frag_end = max(frag_end, ALIGN(frag_start + 1, 1ULL << shift));
Which basically means that we should update just one entry at the time
and then walk the page tables again.
The issue is just that we immediately calculate a new fragment after
each update:
if (frag_start >= frag_end) {
/* figure out the next fragment */
amdgpu_vm_pte_fragment(params,
frag_start, end,
flags, &frag,
&frag_end);
if (frag < shift)
break;
}
And that looks like the place we need to adjust something to allow
updates of the leave nodes.
Alternatively I wouldn't mind having a complete separate function for
unlocked invalidations.
Regards,
Christian.
> entry_end += cursor.pfn & ~(entry_end - 1);
> entry_end = min(entry_end, end);
>
More information about the amd-gfx
mailing list