[V4] drm/xe: Skip clearing purged page-table BOs

[Tejas Upadhyay <tejas.upadhyay@intel.com>]

VRAM page offlining can clear a page-table BO's vmap before VM teardown
calls xe_pt_clear(). Check for a purged BO under its dma-resv lock before
writing to the mapping.

v4(Sashiko):
- dont leave svm notifier lock early
v3(Sashiko):
- Validate NULL vmap
v2(Sashiko):
- Fix lock ordering

Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c | 6 ++++--
 drivers/gpu/drm/xe/xe_vm.c | 4 ++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 7fb2fe1f826c..4b351dbf6572 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -236,9 +236,11 @@ void xe_pt_destroy(struct xe_pt *pt, u32 flags, struct llist_head *deferred)
  */
 void xe_pt_clear(struct xe_device *xe, struct xe_pt *pt)
 {
-	struct iosys_map *map = &pt->bo->vmap;
+	struct xe_bo *bo = pt->bo;
 
-	xe_map_memset(xe, map, 0, 0, SZ_4K);
+	xe_bo_assert_held(bo);
+	if (!iosys_map_is_null(&bo->vmap))
+		xe_map_memset(xe, &bo->vmap, 0, 0, SZ_4K);
 }
 
 /**
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 9e71567b27cc..efa5ff6cc823 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1876,6 +1876,8 @@ static void xe_vm_close(struct xe_vm *vm)
 	bound = drm_dev_enter(&xe->drm, &idx);
 
 	down_write(&vm->lock);
+	xe_vm_lock(vm, false);
+
 	if (xe_vm_in_fault_mode(vm))
 		xe_svm_notifier_lock(vm);
 
@@ -1903,6 +1905,8 @@ static void xe_vm_close(struct xe_vm *vm)
 
 	if (xe_vm_in_fault_mode(vm))
 		xe_svm_notifier_unlock(vm);
+
+	xe_vm_unlock(vm);
 	up_write(&vm->lock);
 
 	if (bound)
-- 
2.52.0