Re: [PATCH 04/13] drm/amdgpu: add amdgpu_vm_pt_leaves()

["Timur Kristóf" <timur.kristof@gmail.com>]

On Thursday, September 17, 2026 1:01:49 PM Central European Summer Time Huang 
Yu wrote:
> From: Christian König <ckoenig.leichtzumerken@gmail.com>
> 
> Add a new function amdgpu_vm_update_leaves() to avoid memory allocation
> on page faults.
> 
> The idea is to only update the leave PDEs/PTEs to let them point to the
> dummy page.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c        | 55 +++++++++++-----
>  .../gpu/drm/amd/amdgpu/amdgpu_vm_internal.h   |  3 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c     | 62 +++++++++++++++++++
>  3 files changed, 105 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c index 5675925ca656..e60143d4990c
> 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -3013,10 +3013,12 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device
> *adev, u32 pasid, u32 vmid, u32 node_id, uint64_t addr,
>  			    uint64_t ts, bool write_fault)
>  {
> +	struct amdgpu_vm_update_params params;
>  	bool is_compute_context = false;
> -	struct drm_exec exec;
> -	uint64_t value, flags;
> +	uint64_t *values, flags;
>  	struct amdgpu_vm *vm;
> +	struct drm_exec exec;
> +	unsigned int idx;
>  	int r;
> 
>  	drm_exec_init(&exec, 0, 1);
> @@ -3060,24 +3062,21 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device
> *adev, u32 pasid, }
> 
>  	addr /= AMDGPU_GPU_PAGE_SIZE;
> -	flags = AMDGPU_PTE_VALID | AMDGPU_PTE_SNOOPED |
> -		AMDGPU_PTE_SYSTEM;
> -
>  	if (is_compute_context) {
>  		/* Intentionally setting invalid PTE flag
>  		 * combination to force a no-retry-fault
>  		 */
>  		flags = AMDGPU_VM_NORETRY_FLAGS;
> -		value = 0;
> +		values = NULL;
>  	} else if (amdgpu_vm_fault_stop == AMDGPU_VM_FAULT_STOP_NEVER) {
>  		/* Redirect the access to the dummy page */
> -		value = adev->dummy_page_addr;
> -		flags |= AMDGPU_PTE_EXECUTABLE | AMDGPU_PTE_READABLE |
> -			AMDGPU_PTE_WRITEABLE;
> -
> +		flags = 0;

Why do you set the flags to zero here?

> +		values = adev->vm_manager.dummy_dst;
>  	} else {
>  		/* Let the hw retry silently on the PTE */
> -		value = 0;
> +		flags = AMDGPU_PTE_VALID | AMDGPU_PTE_SNOOPED |
> +			AMDGPU_PTE_SYSTEM;
> +		values = NULL;
>  	}
> 
>  	r = dma_resv_reserve_fences(vm->root.bo->tbo.base.resv, 1);
> @@ -3086,12 +3085,38 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device
> *adev, u32 pasid, goto error_unlock;
>  	}
> 
> -	r = amdgpu_vm_update_range(adev, vm, true, false, false, false,
> -				   NULL, addr, addr, flags, value, 
0, NULL, NULL, NULL);
> -	if (r)
> +	if (!drm_dev_enter(adev_to_drm(adev), &idx)) {
> +		r = -ENODEV;
>  		goto error_unlock;
> +	}
> 
> -	r = amdgpu_vm_update_pdes(adev, vm, true);
> +	amdgpu_vm_eviction_lock(vm);
> +	if (vm->evicting) {
> +		r = -EBUSY;
> +		goto error_dev_exit;
> +	}
> +
> +	memset(&params, 0, sizeof(params));
> +	params.adev = adev;
> +	params.vm = vm;
> +	params.immediate = true;
> +	params.pages_addr = NULL;
> +
> +	r = vm->update_funcs->prepare(&params, NULL,
> +				      
AMDGPU_KERNEL_JOB_ID_VM_UPDATE_PDES);
> +	if (r)
> +		goto error_dev_exit;
> +
> +	amdgpu_vm_pt_leaves(&params, addr, addr, values, flags);
> +
> +	r = vm->update_funcs->commit(&params, &vm->last_update);


I think this shouldn't pass the last VM update.
Note that amdgpu_vm_sdma_commit() doesn't return a fence anyway when 
params.immediate is true, so I think it's OK to just pass NULL here.



> +	if (r)
> +		goto error_dev_exit;
> +
> +	amdgpu_vm_eviction_unlock(vm);
> +
> +error_dev_exit:
> +	drm_dev_exit(idx);
> 
>  error_unlock:
>  	drm_exec_fini(&exec);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_internal.h
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_internal.h index
> 16cc0d5f5894..7d3c0904e1a1 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_internal.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_internal.h
> @@ -121,6 +121,9 @@ int amdgpu_vm_pde_update(struct amdgpu_vm_update_params
> *params, 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_leaves(struct amdgpu_vm_update_params *params,
> +			 uint64_t start, uint64_t end,
> +			 int64_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);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c index
> 3a6449d60988..2f542c731447 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> @@ -936,6 +936,68 @@ int amdgpu_vm_ptes_update(struct
> amdgpu_vm_update_params *params, return 0;
>  }
> 
> +/**
> + * amdgpu_vm_pt_leaves - update leave PDEs/PTEs

Typo: should be "leaf" instead of "leave".

> + *
> + * @params: see amdgpu_vm_update_params definition
> + * @start: start of GPU address range
> + * @end: end of GPU address range
> + * @dst: optional array with one dst addr per layer
> + * @flags: mapping flags
> + *
> + * Update the leave PDEs/PTEs in the range @start - @end without allocating
> or + * freeing page tables.
> + *
> + * Returns:
> + * 0 for success, negative error code for failure.
> + */
> +void amdgpu_vm_pt_leaves(struct amdgpu_vm_update_params *params,
> +			 uint64_t start, uint64_t end,
> +			 int64_t *dst, uint64_t flags)
> +{
> +	struct amdgpu_device *adev = params->adev;
> +	struct amdgpu_vm_pt_cursor cursor;
> +
> +	amdgpu_vm_pt_start(adev, params->vm, start, &cursor);
> +	while (cursor.pfn < end) {
> +		uint64_t entry_end, pe_start, val;
> +		unsigned int shift, mask;
> +		struct amdgpu_bo *pt;
> +		unsigned int nptes;
> +
> +		/* Walk to the leave entries */
> +		if (amdgpu_vm_pt_descendant(adev, &cursor))
> +			continue;
> +
> +		pt = cursor.parent->bo;
> +		shift = amdgpu_vm_pt_level_shift(adev, cursor.level - 
1);
> +		mask = amdgpu_vm_pt_entries_mask(adev, cursor.level - 
1);
> +
> +		/* Looks good so far, calculate parameters for the 
update */
> +		pe_start = ((cursor.pfn >> shift) & mask) * 8;
> +
> +		entry_end = ((uint64_t)mask + 1) << shift;
> +		entry_end += cursor.pfn & ~(entry_end - 1);
> +		entry_end = min(entry_end, end);
> +
> +		nptes = (entry_end - cursor.pfn) >> shift;
> +		/*
> +		 * This can happen when we set higher level PDEs to 
unmap and/or
> +		 * silent to stop fault floods.
> +		 */
> +		nptes = max(nptes, 1u);
> +
> +		val = dst ? dst[cursor.level] : 0;
> +		trace_amdgpu_vm_update_ptes(params, cursor.pfn, 
entry_end,
> +					    min(nptes, 32u), 
val, 0, flags);
> +
> +		params->vm->update_funcs->update(params, 
to_amdgpu_bo_vm(pt),
> +						 pe_start, 
val, nptes, 0,
> +						 flags);
> +		amdgpu_vm_pt_next(adev, &cursor);
> +	}
> +}
> +
>  /**
>   * amdgpu_vm_pt_map_tables - have bo of root PD cpu accessible
>   * @adev: amdgpu device structure