Re: [PATCH v9 2/2] drm/amdgpu: sync page table freeing with tlb flush

[Christian König <christian.koenig@xxxxxxx>]

Am 18.03.24 um 17:11 schrieb Shashank Sharma:
> The idea behind this patch is to delay the freeing of PT entry objects
> until the TLB flush is done.
>
> This patch:
> - Adds a tlb_flush_waitlist in amdgpu_vm_update_params which will keep the
>    objects that need to be freed after tlb_flush.
> - Adds PT entries in this list in amdgpu_vm_ptes_update after finding
>    the PT entry.
> - Changes functionality of amdgpu_vm_pt_free_dfs from (df_search + free)
>    to simply freeing of the BOs, also renames it to
>    amdgpu_vm_pt_free_list to reflect this same.
> - Exports function amdgpu_vm_pt_free_list to be called directly.
> - Calls amdgpu_vm_pt_free_list directly from amdgpu_vm_update_range.
>
> V2: rebase
> V4: Addressed review comments from Christian
>      - add only locked PTEs entries in TLB flush waitlist.
>      - do not create a separate function for list flush.
>      - do not create a new lock for TLB flush.
>      - there is no need to wait on tlb_flush_fence exclusively.
>
> V5: Addressed review comments from Christian
>      - change the amdgpu_vm_pt_free_dfs's functionality to simple freeing
>        of the objects and rename it.
>      - add all the PTE objects in params->tlb_flush_waitlist
>      - let amdgpu_vm_pt_free_root handle the freeing of BOs independently
>      - call amdgpu_vm_pt_free_list directly
>
> V6: Rebase
> V7: Rebase
> V8: Added a NULL check to fix this backtrace issue:
> [  415.351447] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [  415.359245] #PF: supervisor write access in kernel mode
> [  415.365081] #PF: error_code(0x0002) - not-present page
> [  415.370817] PGD 101259067 P4D 101259067 PUD 10125a067 PMD 0
> [  415.377140] Oops: 0002 [#1] PREEMPT SMP NOPTI
> [  415.382004] CPU: 0 PID: 25481 Comm: test_with_MPI.e Tainted: G           OE     5.18.2-mi300-build-140423-ubuntu-22.04+ #24
> [  415.394437] Hardware name: AMD Corporation Sh51p/Sh51p, BIOS RMO1001AS 02/21/2024
> [  415.402797] RIP: 0010:amdgpu_vm_ptes_update+0x6fd/0xa10 [amdgpu]
> [  415.409648] Code: 4c 89 ff 4d 8d 66 30 e8 f1 ed ff ff 48 85 db 74 42 48 39 5d a0 74 40 48 8b 53 20 48 8b 4b 18 48 8d 43 18 48 8d 75 b0 4c 89 ff <48
> > 89 51 08 48 89 0a 49 8b 56 30 48 89 42 08 48 89 53 18 4c 89 63
> [  415.430621] RSP: 0018:ffffc9000401f990 EFLAGS: 00010287
> [  415.436456] RAX: ffff888147bb82f0 RBX: ffff888147bb82d8 RCX: 0000000000000000
> [  415.444426] RDX: 0000000000000000 RSI: ffffc9000401fa30 RDI: ffff888161f80000
> [  415.452397] RBP: ffffc9000401fa80 R08: 0000000000000000 R09: ffffc9000401fa00
> [  415.460368] R10: 00000007f0cc0000 R11: 00000007f0c85000 R12: ffffc9000401fb20
> [  415.468340] R13: 00000007f0d00000 R14: ffffc9000401faf0 R15: ffff888161f80000
> [  415.476312] FS:  00007f132ff89840(0000) GS:ffff889f87c00000(0000) knlGS:0000000000000000
> [  415.485350] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  415.491767] CR2: 0000000000000008 CR3: 0000000161d46003 CR4: 0000000000770ef0
> [  415.499738] PKRU: 55555554
> [  415.502750] Call Trace:
> [  415.505482]  <TASK>
> [  415.507825]  amdgpu_vm_update_range+0x32a/0x880 [amdgpu]
> [  415.513869]  amdgpu_vm_clear_freed+0x117/0x250 [amdgpu]
> [  415.519814]  amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu+0x18c/0x250 [amdgpu]
> [  415.527729]  kfd_ioctl_unmap_memory_from_gpu+0xed/0x340 [amdgpu]
> [  415.534551]  kfd_ioctl+0x3b6/0x510 [amdgpu]
>
> V9: Addressed review comments from Christian
>      - No NULL check reqd for root PT freeing
>      - Free PT list regardless of needs_flush
>      - Move adding BOs in list in a separate function
>
> Cc: Christian König <Christian.Koenig@xxxxxxx>
> Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> Cc: Felix Kuehling <felix.kuehling@xxxxxxx>
> Cc: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
> Acked-by: Felix Kuehling <felix.kuehling@xxxxxxx>
> Acked-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
> Tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
> Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  3 ++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h    |  7 +++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 66 +++++++++++++++--------
>   3 files changed, 53 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index 104bf600c85f..8fada1152664 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -986,6 +986,7 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
>   	params.unlocked = unlocked;
>   	params.needs_flush = flush_tlb;
>   	params.allow_override = allow_override;
> +	INIT_LIST_HEAD(&params.tlb_flush_waitlist);
>   
>   	/* Implicitly sync to command submissions in the same VM before
>   	 * unmapping. Sync to moving fences before mapping.
> @@ -1076,6 +1077,8 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
>   		tlb_cb = NULL;
>   	}
>   
> +	amdgpu_vm_pt_free_list(adev, &params);
> +
>   error_free:
>   	kfree(tlb_cb);
>   	amdgpu_vm_eviction_unlock(vm);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> index b0a4fe683352..54d7da396de0 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> @@ -266,6 +266,11 @@ struct amdgpu_vm_update_params {
>   	 * to be overridden for NUMA local memory.
>   	 */
>   	bool allow_override;
> +
> +	/**
> +	 * @tlb_flush_waitlist: temporary storage for BOs until tlb_flush
> +	 */
> +	struct list_head tlb_flush_waitlist;
>   };
>   
>   struct amdgpu_vm_update_funcs {
> @@ -547,6 +552,8 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
>   			  uint64_t start, uint64_t end,
>   			  uint64_t dst, uint64_t flags);
>   void amdgpu_vm_pt_free_work(struct work_struct *work);
> +void amdgpu_vm_pt_free_list(struct amdgpu_device *adev,
> +			    struct amdgpu_vm_update_params *params);
>   
>   #if defined(CONFIG_DEBUG_FS)
>   void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct seq_file *m);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> index 601df0ce8290..d904fc96ba0f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> @@ -622,40 +622,58 @@ void amdgpu_vm_pt_free_work(struct work_struct *work)
>   }
>   
>   /**
> - * amdgpu_vm_pt_free_dfs - free PD/PT levels
> + * amdgpu_vm_pt_free_list - free PD/PT levels
>    *
>    * @adev: amdgpu device structure
> - * @vm: amdgpu vm structure
> - * @start: optional cursor where to start freeing PDs/PTs
> - * @unlocked: vm resv unlock status
> + * @params: see amdgpu_vm_update_params definition
>    *
> - * Free the page directory or page table level and all sub levels.
> + * Free the page directory objects saved in the flush list
>    */
> -static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
> -				  struct amdgpu_vm *vm,
> -				  struct amdgpu_vm_pt_cursor *start,
> -				  bool unlocked)
> +void amdgpu_vm_pt_free_list(struct amdgpu_device *adev,
> +			    struct amdgpu_vm_update_params *params)
>   {
> -	struct amdgpu_vm_pt_cursor cursor;
> -	struct amdgpu_vm_bo_base *entry;
> +	struct amdgpu_vm_bo_base *entry, *next;
> +	struct amdgpu_vm *vm = params->vm;
> +	bool unlocked = params->unlocked;
> +
> +	if (list_empty(&params->tlb_flush_waitlist))
> +		return;
>   
>   	if (unlocked) {
>   		spin_lock(&vm->status_lock);
> -		for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
> -			list_move(&entry->vm_status, &vm->pt_freed);
> -
> -		if (start)
> -			list_move(&start->entry->vm_status, &vm->pt_freed);
> +		list_splice_init(&vm->pt_freed, &params->tlb_flush_waitlist);
>   		spin_unlock(&vm->status_lock);
>   		schedule_work(&vm->pt_free_work);
>   		return;
>   	}
>   
> -	for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
> +	list_for_each_entry_safe(entry, next, &params->tlb_flush_waitlist, vm_status)
>   		amdgpu_vm_pt_free(entry);
> +}
>   
> -	if (start)
> -		amdgpu_vm_pt_free(start->entry);
> +/**
> + * amdgpu_vm_pt_add_list - add PD/PT level to the flush list
> + *
> + * @params: parameters for the update
> + * @cursor: first PT entry to start DF search from, non NULL
> + *
> + * This list will be freed after TLB flush.
> + */
> +static void amdgpu_vm_pt_add_list(struct amdgpu_vm_update_params *params,
> +				  struct amdgpu_vm_pt_cursor *cursor)
> +{
> +	struct amdgpu_vm_pt_cursor seek;
> +	struct amdgpu_vm_bo_base *entry;
> +
> +	spin_lock(&params->vm->status_lock);
> +	for_each_amdgpu_vm_pt_dfs_safe(params->adev, params->vm, cursor, seek, entry) {
> +		if (entry && entry->bo)
> +			list_move(&entry->vm_status, &params->tlb_flush_waitlist);
> +	}
> +
> +	/* enter start node now */
> +	list_move(&cursor->entry->vm_status, &params->tlb_flush_waitlist);
> +	spin_unlock(&params->vm->status_lock);
>   }
>   
>   /**
> @@ -667,7 +685,11 @@ static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
>    */
>   void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct amdgpu_vm *vm)
>   {
> -	amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
> +	struct amdgpu_vm_pt_cursor cursor;
> +	struct amdgpu_vm_bo_base *entry;
> +
> +	for_each_amdgpu_vm_pt_dfs_safe(adev, vm, NULL, cursor, entry)
> +		amdgpu_vm_pt_free(entry);
>   }
>   
>   /**
> @@ -973,9 +995,7 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
>   				/* Make sure previous mapping is freed */
>   				if (cursor.entry->bo) {
>   					params->needs_flush = true;
> -					amdgpu_vm_pt_free_dfs(adev, params->vm,
> -							      &cursor,
> -							      params->unlocked);
> +					amdgpu_vm_pt_add_list(params, &cursor);
>   				}
>   				amdgpu_vm_pt_next(adev, &cursor);
>   			}