Re: [PATCH v4 7/8] drm/xe/madvise: Block imported and exported dma-bufs

Matthew Brost
2026-01-20T17:51:48Z

On Tue, Jan 20, 2026 at 11:38:53AM +0530, Arvind Yadav wrote:
> Prevent marking imported or exported dma-bufs as purgeable.
> External devices may be accessing these buffers without our
> knowledge, making purging unsafe.
>
> Check drm_gem_is_imported() for buffers created by other
> drivers and obj->dma_buf for buffers exported to other
> drivers. Silently skip these BOs during madvise processing.
>
> This follows drm_gem_shmem's purgeable implementation and
> prevents data corruption from purging actively-used shared
> buffers.
>
> v3:
> - Addresses review feedback from Matt Roper about handling
> imported/exported BOs correctly in the purgeable BO
> implementation.
>
> v4:
> - Check should be add to xe_vm_madvise_purgeable_bo.
>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>

@Thomas - couple questions below here I need a 2nd opinion on.

> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> ---
> drivers/gpu/drm/xe/xe_vm_madvise.c | 33 ++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
> index 27b6ad65b314..5808fef89777 100644
> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> @@ -180,6 +180,31 @@ static void madvise_pat_index(struct xe_device *xe, struct xe_vm *vm,
> }
> }
>
> +/**
> + * xe_bo_is_external_dmabuf() - Check if BO is imported or exported dma-buf
> + * @bo: Buffer object
> + *
> + * Prevent marking imported or exported dma-bufs as purgeable.
> + * External devices may be accessing these buffers without our
> + * knowledge, making purging unsafe.
> + *
> + * Return: true if BO is imported or exported, false otherwise
> + */
> +static bool xe_bo_is_external_dmabuf(struct xe_bo *bo)
> +{

@Thomas

Should we have this check more generic? e.g., if a BO is not tied to a
VM, we don't allow purablity to be set?

> + struct drm_gem_object *obj = &bo->ttm.base;
> +
> + /* Imported from another driver */
> + if (drm_gem_is_imported(obj))
> + return true;
> +
> + /* Exported to another driver */
> + if (obj->dma_buf)
> + return true;
> +
> + return false;
> +}
> +
> /**
> * xe_bo_all_vmas_dontneed() - Check if all VMAs of a BO are marked DONTNEED
> * @bo: Buffer object
> @@ -200,6 +225,10 @@ static bool xe_bo_all_vmas_dontneed(struct xe_bo *bo)
>
> dma_resv_assert_held(bo->ttm.base.resv);
>
> + /* External dma-bufs cannot be purgeable */
> + if (xe_bo_is_external_dmabuf(bo))
> + return false;
> +
> drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
> drm_gpuvm_bo_for_each_va(gpuva, vm_bo) {
> struct xe_vma *vma = gpuva_to_vma(gpuva);
> @@ -277,6 +306,10 @@ static bool xe_vm_madvise_purgeable_bo(struct xe_device *xe, struct xe_vm *vm,
> /* BO must be locked before modifying madv state */
> xe_bo_assert_held(bo);
>
> + /* Skip external dma-bufs */
> + if (xe_bo_is_external_dmabuf(bo))
> + continue;

@Thomas

I think instead of silently continuing here we fail the IOCTL with
-EINVAL?

What do you think?

Matt

> +
> /*
> * Once purged, always purged. Cannot transition back to WILLNEED.
> * This matches i915 semantics where purged BOs are permanently invalid.
> --
> 2.43.0
>