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drm/xe/vm: nuke PTs only after unlinking contested VMAs

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In xe_vm_close_and_put(), external-BO VMAs are queued on the contested
list for deferred destruction via xe_vma_destroy_unlocked(). However,
xe_vm_pt_destroy() was previously invoked before processing contested
VMAs, destroying vm->pt_root while those VMAs were still linked to their
respective buffer objects (vm_bo->list.gpuva).

If a concurrent thread evicts one of those shared buffer objects,
xe_bo_trigger_rebind() holding only bo->resv walks the BO's VMAs and, in
fault mode, calls xe_vm_invalidate_vma() -> xe_pt_zap_ptes(). Because
vm->pt_root[tile->id] is already NULL, dereferencing pt->level causes a
NULL ptr deref.

Fix this by deferring xe_vm_free_scratch() and xe_vm_pt_destroy() until
after all contested VMAs have been unlinked and destroyed.

User is reporting hitting a NULL ptr deref in xe_pt_zap_ptes(), which
could be explained by this race.

Assisted-by: LLM
Fixes: b06d47be7c ("drm/xe: Port Xe to GPUVA")
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/9290
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260918131034.598078-2-matthew.auld@intel.com
(cherry picked from commit c286364895)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Matthew Auld 2026-09-18 14:10:35 +01:00 • committed by Rodrigo Vivi
commit 24a22fb3c7
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1 changed files with 9 additions and 12 deletions
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