Re: [RFC v2 5/9] drm/xe/bo: Handle CPU faults on purged buffer objects

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

On Mon, Dec 01, 2025 at 11:20:15AM +0530, Arvind Yadav wrote:
> Modify the CPU page fault handler, `xe_bo_cpu_fault()`, to correctly
> handle access to buffer objects that have been purged.
> 
> When a buffer object is in the `XE_MADV_PURGED` state, its backing
> store has been reclaimed by the kernel. If the CPU attempts to access
> this memory, it is an error that should be reported to the application.
> 
> v2:
>   - Added xe_bo_is_purged(bo) instead of atomic_read.
>   - Avoids leaks and keeps drm_dev_exit() while returning.
> 
> Cc: Matthew Brost <matthew.brost@intel.com>

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

> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_bo.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index f0b3f7a13114..7f5bcf114ed4 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1992,6 +1992,16 @@ static vm_fault_t xe_bo_cpu_fault(struct vm_fault *vmf)
>  	if (!drm_dev_enter(&xe->drm, &idx))
>  		return ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot);
>  
> +	/*
> +	 * BO content is gone. Signal the user process.
> +	 * Once purged, BO remains permanently invalid (i915 semantics).
> +	 * Application must destroy and recreate the BO.
> +	 */
> +	if (xe_bo_is_purged(bo)) {
> +		ret = VM_FAULT_SIGBUS;
> +		goto out;
> +	}
> +
>  	ret = xe_bo_cpu_fault_fastpath(vmf, xe, bo, needs_rpm);
>  	if (ret != VM_FAULT_RETRY)
>  		goto out;
> -- 
> 2.43.0
>