Re: [PATCH v5 20/25] drm/xe/bo: Update atomic_access attribute on madvise

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Jul 30, 2025 at 06:30:45PM +0530, Himal Prasad Ghimiray wrote:
> Update the bo_atomic_access based on user-provided input and determine
> the migration to smem during a CPU fault
> 
> v2 (Matthew Brost)
> - Avoid cpu unmapping if bo is already in smem
> - check atomics on smem too for ioctl
> - Add comments
> 
> v3
> - Avoid migration in prefetch
> 
> v4 (Matthew Brost)
> - make sanity check function bool
> - add assert for smem placement
> - fix doc
> 
> v5 (Matthew Brost)
> - NACK atomic fault with  DRM_XE_ATOMIC_CPU
> 
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_bo.c           | 29 ++++++++++++--
>  drivers/gpu/drm/xe/xe_gt_pagefault.c | 35 ++++++----------
>  drivers/gpu/drm/xe/xe_vm.c           |  7 +++-
>  drivers/gpu/drm/xe/xe_vm_madvise.c   | 60 +++++++++++++++++++++++++++-
>  4 files changed, 103 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index ffca1cea5585..6ab297f94d12 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1709,6 +1709,18 @@ static void xe_gem_object_close(struct drm_gem_object *obj,
>  	}
>  }
>  
> +static bool should_migrate_to_smem(struct xe_bo *bo)
> +{
> +	/*
> +	 * NOTE: The following atomic checks are platform-specific. For example,
> +	 * if a device supports CXL atomics, these may not be necessary or
> +	 * may behave differently.
> +	 */
> +
> +	return bo->attr.atomic_access == DRM_XE_ATOMIC_GLOBAL ||
> +	       bo->attr.atomic_access == DRM_XE_ATOMIC_CPU;
> +}
> +
>  static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
>  {
>  	struct ttm_buffer_object *tbo = vmf->vma->vm_private_data;
> @@ -1717,7 +1729,7 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
>  	struct xe_bo *bo = ttm_to_xe_bo(tbo);
>  	bool needs_rpm = bo->flags & XE_BO_FLAG_VRAM_MASK;
>  	vm_fault_t ret;
> -	int idx;
> +	int idx, r = 0;
>  
>  	if (needs_rpm)
>  		xe_pm_runtime_get(xe);
> @@ -1729,8 +1741,19 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
>  	if (drm_dev_enter(ddev, &idx)) {
>  		trace_xe_bo_cpu_fault(bo);
>  
> -		ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> -					       TTM_BO_VM_NUM_PREFAULT);
> +		if (should_migrate_to_smem(bo)) {
> +			xe_assert(xe, bo->flags & XE_BO_FLAG_SYSTEM);
> +
> +			r = xe_bo_migrate(bo, XE_PL_TT);
> +			if (r == -EBUSY || r == -ERESTARTSYS || r == -EINTR)
> +				ret = VM_FAULT_NOPAGE;
> +			else if (r)
> +				ret = VM_FAULT_SIGBUS;
> +		}
> +		if (!ret)
> +			ret = ttm_bo_vm_fault_reserved(vmf,
> +						       vmf->vma->vm_page_prot,
> +						       TTM_BO_VM_NUM_PREFAULT);
>  		drm_dev_exit(idx);
>  	} else {
>  		ret = ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot);
> diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> index ab43dec52776..4ea30fbce9bd 100644
> --- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> @@ -75,7 +75,7 @@ static bool vma_is_valid(struct xe_tile *tile, struct xe_vma *vma)
>  }
>  
>  static int xe_pf_begin(struct drm_exec *exec, struct xe_vma *vma,
> -		       bool atomic, struct xe_vram_region *vram)
> +		       bool need_vram_move, struct xe_vram_region *vram)
>  {
>  	struct xe_bo *bo = xe_vma_bo(vma);
>  	struct xe_vm *vm = xe_vma_vm(vma);
> @@ -85,26 +85,13 @@ static int xe_pf_begin(struct drm_exec *exec, struct xe_vma *vma,
>  	if (err)
>  		return err;
>  
> -	if (atomic && vram) {
> -		xe_assert(vm->xe, IS_DGFX(vm->xe));
> +	if (!bo)
> +		return 0;
>  
> -		if (xe_vma_is_userptr(vma)) {
> -			err = -EACCES;
> -			return err;
> -		}
> +	err = need_vram_move ? xe_bo_migrate(bo, vram->placement) :
> +			       xe_bo_validate(bo, vm, true);
>  
> -		/* Migrate to VRAM, move should invalidate the VMA first */
> -		err = xe_bo_migrate(bo, vram->placement);
> -		if (err)
> -			return err;
> -	} else if (bo) {
> -		/* Create backing store if needed */
> -		err = xe_bo_validate(bo, vm, true);
> -		if (err)
> -			return err;
> -	}
> -
> -	return 0;
> +	return err;
>  }
>  
>  static int handle_vma_pagefault(struct xe_gt *gt, struct xe_vma *vma,
> @@ -115,10 +102,14 @@ static int handle_vma_pagefault(struct xe_gt *gt, struct xe_vma *vma,
>  	struct drm_exec exec;
>  	struct dma_fence *fence;
>  	ktime_t end = 0;
> -	int err;
> +	int err, needs_vram;
>  
>  	lockdep_assert_held_write(&vm->lock);
>  
> +	needs_vram = xe_vma_need_vram_for_atomic(vm->xe, vma, atomic);
> +	if (needs_vram < 0 || (needs_vram && xe_vma_is_userptr(vma)))
> +		return needs_vram < 0 ? needs_vram : -EACCES;
> +
>  	xe_gt_stats_incr(gt, XE_GT_STATS_ID_VMA_PAGEFAULT_COUNT, 1);
>  	xe_gt_stats_incr(gt, XE_GT_STATS_ID_VMA_PAGEFAULT_KB, xe_vma_size(vma) / 1024);
>  
> @@ -141,7 +132,7 @@ static int handle_vma_pagefault(struct xe_gt *gt, struct xe_vma *vma,
>  	/* Lock VM and BOs dma-resv */
>  	drm_exec_init(&exec, 0, 0);
>  	drm_exec_until_all_locked(&exec) {
> -		err = xe_pf_begin(&exec, vma, atomic, tile->mem.vram);
> +		err = xe_pf_begin(&exec, vma, needs_vram == 1, tile->mem.vram);
>  		drm_exec_retry_on_contention(&exec);
>  		if (xe_vm_validate_should_retry(&exec, err, &end))
>  			err = -EAGAIN;
> @@ -576,7 +567,7 @@ static int handle_acc(struct xe_gt *gt, struct acc *acc)
>  	/* Lock VM and BOs dma-resv */
>  	drm_exec_init(&exec, 0, 0);
>  	drm_exec_until_all_locked(&exec) {
> -		ret = xe_pf_begin(&exec, vma, true, tile->mem.vram);
> +		ret = xe_pf_begin(&exec, vma, IS_DGFX(vm->xe), tile->mem.vram);
>  		drm_exec_retry_on_contention(&exec);
>  		if (ret)
>  			break;
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index d57fc1071142..0774b40bc37b 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -4214,15 +4214,18 @@ void xe_vm_snapshot_free(struct xe_vm_snapshot *snap)
>   */
>  int xe_vma_need_vram_for_atomic(struct xe_device *xe, struct xe_vma *vma, bool is_atomic)
>  {
> +	u32 atomic_access = xe_vma_bo(vma) ? xe_vma_bo(vma)->attr.atomic_access :
> +					     vma->attr.atomic_access;
> +
>  	if (!IS_DGFX(xe) || !is_atomic)
> -		return 0;
> +		return false;
>  
>  	/*
>  	 * NOTE: The checks implemented here are platform-specific. For
>  	 * instance, on a device supporting CXL atomics, these would ideally
>  	 * work universally without additional handling.
>  	 */
> -	switch (vma->attr.atomic_access) {
> +	switch (atomic_access) {
>  	case DRM_XE_ATOMIC_DEVICE:
>  		return !xe->info.has_device_atomics_on_smem;
>  
> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
> index 51a9364abc72..16ab1267ad21 100644
> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> @@ -102,6 +102,7 @@ static void madvise_atomic(struct xe_device *xe, struct xe_vm *vm,
>  			   struct xe_vma **vmas, int num_vmas,
>  			   struct drm_xe_madvise *op)
>  {
> +	struct xe_bo *bo;
>  	int i;
>  
>  	xe_assert(vm->xe, op->type == DRM_XE_MEM_RANGE_ATTR_ATOMIC);
> @@ -113,8 +114,21 @@ static void madvise_atomic(struct xe_device *xe, struct xe_vm *vm,
>  			      xe->info.has_device_atomics_on_smem))
>  				continue;
>  		}
> +
>  		vmas[i]->attr.atomic_access = op->atomic.val;
> -	/*TODO: handle bo backed vmas */
> +
> +		bo = xe_vma_bo(vmas[i]);
> +		if (!bo)
> +			continue;
> +
> +		xe_bo_assert_held(bo);
> +		bo->attr.atomic_access = op->atomic.val;
> +
> +		/* Invalidate cpu page table, so bo can migrate to smem in next access */
> +		if (xe_bo_is_vram(bo) &&
> +		    (bo->attr.atomic_access == DRM_XE_ATOMIC_CPU ||
> +		     bo->attr.atomic_access == DRM_XE_ATOMIC_GLOBAL))
> +			ttm_bo_unmap_virtual(&bo->ttm);
>  	}
>  }
>  
> @@ -263,6 +277,41 @@ static bool madvise_args_are_sane(struct xe_device *xe, const struct drm_xe_madv
>  	return true;
>  }
>  
> +static bool check_bo_args_are_sane(struct xe_vm *vm, struct xe_vma **vmas,
> +				   int num_vmas, u32 atomic_val)
> +{
> +	struct xe_device *xe = vm->xe;
> +	struct xe_bo *bo;
> +	int i;
> +
> +	for (i = 0; i < num_vmas; i++) {
> +		bo = xe_vma_bo(vmas[i]);
> +		if (!bo)
> +			continue;
> +		/*
> +		 * NOTE: The following atomic checks are platform-specific. For example,
> +		 * if a device supports CXL atomics, these may not be necessary or
> +		 * may behave differently.
> +		 */
> +		if (XE_IOCTL_DBG(xe, atomic_val == DRM_XE_ATOMIC_CPU &&
> +				 !(bo->flags & XE_BO_FLAG_SYSTEM)))
> +			return false;
> +
> +		if (XE_IOCTL_DBG(xe, atomic_val == DRM_XE_ATOMIC_DEVICE &&
> +				 !(bo->flags & XE_BO_FLAG_VRAM0) &&
> +				 !(bo->flags & XE_BO_FLAG_VRAM1) &&
> +				 !(bo->flags & XE_BO_FLAG_SYSTEM &&
> +				   xe->info.has_device_atomics_on_smem)))
> +			return false;
> +
> +		if (XE_IOCTL_DBG(xe, atomic_val == DRM_XE_ATOMIC_GLOBAL &&
> +				 (!(bo->flags & XE_BO_FLAG_SYSTEM) ||
> +				  (!(bo->flags & XE_BO_FLAG_VRAM0) &&
> +				   !(bo->flags & XE_BO_FLAG_VRAM1)))))
> +			return false;
> +	}
> +	return true;
> +}
>  /**
>   * xe_vm_madvise_ioctl - Handle MADVise ioctl for a VM
>   * @dev: DRM device pointer
> @@ -314,6 +363,15 @@ int xe_vm_madvise_ioctl(struct drm_device *dev, void *data, struct drm_file *fil
>  		goto unlock_vm;
>  
>  	if (madvise_range.has_bo_vmas) {
> +		if (args->type == DRM_XE_MEM_RANGE_ATTR_ATOMIC) {
> +			if (!check_bo_args_are_sane(vm, madvise_range.vmas,
> +						    madvise_range.num_vmas,
> +						    args->atomic.val)) {
> +				err = -EINVAL;
> +				goto unlock_vm;
> +			}
> +		}
> +
>  		drm_exec_init(&exec, DRM_EXEC_IGNORE_DUPLICATES | DRM_EXEC_INTERRUPTIBLE_WAIT, 0);
>  		drm_exec_until_all_locked(&exec) {
>  			for (int i = 0; i < madvise_range.num_vmas; i++) {
> -- 
> 2.34.1
>