From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Matthew Auld <matthew.auld@intel.com>,
	=?UTF-8?q?Thomas=20Hellstr=C3=B6m?= <thomas.hellstrom@linux.intel.com>,
	Matthew Brost <matthew.brost@intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12.y] drm/xe/vm: nuke PTs only after unlinking contested VMAs
Date: Tue, 29 Sep 2026 14:47:01 -0400
Message-ID: <20260929184701.522410-1-sashal@kernel.org>
In-Reply-To: <2026092919-qualm-steadily-7858@gregkh>
References: <2026092919-qualm-steadily-7858@gregkh>
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From: Matthew Auld <matthew.auld@intel.com>

[ Upstream commit 24a22fb3c731474b68e986af6804db450fb88617 ]

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: b06d47be7c83 ("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 c2863648959489767f08892fd6e90577d2ea0b6a)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[ adapted xe_vm_pt_destroy() cleanup to the existing inline page-table destruction loop. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/xe/xe_vm.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index deb4d0314db3a..fa0d7c6414022 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1678,13 +1678,21 @@ void xe_vm_close_and_put(struct xe_vm *vm)
 		vma->gpuva.flags |= XE_VMA_DESTROYED;
 	}
 
+	xe_vm_unlock(vm);
+
 	/*
-	 * All vm operations will add shared fences to resv.
-	 * The only exception is eviction for a shared object,
-	 * but even so, the unbind when evicted would still
-	 * install a fence to resv. Hence it's safe to
-	 * destroy the pagetables immediately.
+	 * Unlink and destroy all contested external-BO VMAs before destroying
+	 * the page tables. Otherwise, concurrent eviction holding only bo->resv
+	 * can walk the BO's VMAs and attempt to invalidate/zap page tables that
+	 * have already been freed.
 	 */
+	list_for_each_entry_safe(vma, next_vma, &contested,
+				 combined_links.destroy) {
+		list_del_init(&vma->combined_links.destroy);
+		xe_vma_destroy_unlocked(vma);
+	}
+
+	xe_vm_lock(vm, false);
 	xe_vm_free_scratch(vm);
 
 	for_each_tile(tile, xe, id) {
@@ -1695,17 +1703,6 @@ void xe_vm_close_and_put(struct xe_vm *vm)
 	}
 	xe_vm_unlock(vm);
 
-	/*
-	 * VM is now dead, cannot re-add nodes to vm->vmas if it's NULL
-	 * Since we hold a refcount to the bo, we can remove and free
-	 * the members safely without locking.
-	 */
-	list_for_each_entry_safe(vma, next_vma, &contested,
-				 combined_links.destroy) {
-		list_del_init(&vma->combined_links.destroy);
-		xe_vma_destroy_unlocked(vma);
-	}
-
 	up_write(&vm->lock);
 
 	down_write(&xe->usm.lock);
-- 
2.53.0