1 files changed, 29 insertions, 4 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 8d53ed2..429d526 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1013,13 +1013,38 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
 	}
 	/* Add the persistent grant into the list of free grants */
 	for (i = 0; i < nseg; i++) {
-		list_add(&s->grants_used[i]->node, &info->persistent_gnts);
-		info->persistent_gnts_c++;
+		if (gnttab_query_foreign_access(s->grants_used[i]->gref)) {
+			/*
+			 * If the grant is still mapped by the backend (the
+			 * backend has chosen to make this grant persistent)
+			 * we add it at the head of the list, so it will be
+			 * reused first.
+			 */
+			list_add(&s->grants_used[i]->node, &info->persistent_gnts);
+			info->persistent_gnts_c++;
+		} else {
+			/*
+			 * If the grant is not mapped by the backend we end the
+			 * foreign access and add it to the tail of the list,
+			 * so it will not be picked again unless we run out of
+			 * persistent grants.
+			 */
+			gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
+			s->grants_used[i]->gref = GRANT_INVALID_REF;
+			list_add_tail(&s->grants_used[i]->node, &info->persistent_gnts);
+		}
 	}
 	if (s->req.operation == BLKIF_OP_INDIRECT) {
 		for (i = 0; i < INDIRECT_GREFS(nseg); i++) {
-			list_add(&s->indirect_grants[i]->node, &info->persistent_gnts);
-			info->persistent_gnts_c++;
+			if (gnttab_query_foreign_access(s->indirect_grants[i]->gref)) {
+				list_add(&s->indirect_grants[i]->node, &info->persistent_gnts);
+				info->persistent_gnts_c++;
+			} else {
+				gnttab_end_foreign_access(s->indirect_grants[i]->gref, 0, 0UL);
+				s->indirect_grants[i]->gref = GRANT_INVALID_REF;
+				list_add_tail(&s->indirect_grants[i]->node,
+				              &info->persistent_gnts);
+			}
 		}
 	}
 }