CVE-2026-72358: In the Linux kernel, the following vulnerability has been resolved: drm/xe/pt: prevent invalid cursor access for purged

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/pt: prevent invalid cursor access for purged BOs

During a page table walk for binding, xe_pt_stage_bind() explicitly skips initializing the xe_res_cursor for purged BOs, treating them similarly to NULL VMAs by only setting the cursor size.

However, xe_pt_hugepte_possible() and xe_pt_scan_64K() did not check if the BO was purged before attempting to walk the cursor using xe_res_dma() and xe_res_next(). Because the cursor was left uninitialized for purged BOs, this falls through and triggers warnings like:

WARNING: drivers/gpu/drm/xe/xe_res_cursor.h:274 at xe_res_next

Fix this by explicitly checking if the BO is purged in both xe_pt_hugepte_possible() and xe_pt_scan_64K(), returning early just as we do for NULL VMAs, avoiding the invalid cursor accesses entirely.

As a precaution, also zero-initialize the cursor in xe_pt_stage_bind() to ensure we don't pass garbage data into the page table walkers if we ever hit a similar edge case in the future.

(cherry picked from commit 4c7b9c6ece32440e5a435a92076d049450cd2d2e)