drm/xe: prevent potential UAF in pf_provision_vf_ggtt()

The node ptr can point to an already freed ptr, if we hit the path with
an already allocated node. We later dereference that pointer with:

	xe_gt_assert(gt, !xe_ggtt_node_allocated(node));

which is a potential UAF. Fix this by not stashing the ptr for node.
Also since it is likely a bad idea to leave config->ggtt_region pointing
to a stale ptr, also set that to NULL by calling
pf_release_vf_config_ggtt() instead of pf_release_ggtt().

Fixes: 34e80422 ("drm/xe: Make xe_ggtt_node struct independent")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240828104341.180111-2-matthew.auld@intel.com
(cherry picked from commit 89076b5a8b4e0a01040585e156a0b014cd472fd3)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

drivers/gpu/drm/xe/xe_gt_sriov_pf_config.c

@@ -399,7 +399,7 @@ static void pf_release_vf_config_ggtt(struct xe_gt *gt, struct xe_gt_sriov_confi
 static int pf_provision_vf_ggtt(struct xe_gt *gt, unsigned int vfid, u64 size)
 {
 	struct xe_gt_sriov_config *config = pf_pick_vf_config(gt, vfid);
-	struct xe_ggtt_node *node = config->ggtt_region;
+	struct xe_ggtt_node *node;
 	struct xe_tile *tile = gt_to_tile(gt);
 	struct xe_ggtt *ggtt = tile->mem.ggtt;
 	u64 alignment = pf_get_ggtt_alignment(gt);
@@ -411,14 +411,14 @@ static int pf_provision_vf_ggtt(struct xe_gt *gt, unsigned int vfid, u64 size)
 
 	size = round_up(size, alignment);
 
-	if (xe_ggtt_node_allocated(node)) {
+	if (xe_ggtt_node_allocated(config->ggtt_region)) {
 		err = pf_distribute_config_ggtt(tile, vfid, 0, 0);
 		if (unlikely(err))
 			return err;
 
-		pf_release_ggtt(tile, node);
+		pf_release_vf_config_ggtt(gt, config);
 	}
-	xe_gt_assert(gt, !xe_ggtt_node_allocated(node));
+	xe_gt_assert(gt, !xe_ggtt_node_allocated(config->ggtt_region));
 
 	if (!size)
 		return 0;