xen-gntdev: Avoid unmapping ranges twice

In paravirtualized domains, mn_invl_page or mn_invl_range_start can
unmap a segment of a mapped region without unmapping all pages. When
the region is later released, the pages will be unmapped twice, leading
to an incorrect -EINVAL return.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 31 insertions, 2 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 4ca4262d3d19..4687cd557c97 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -282,7 +282,7 @@ static int map_grant_pages(struct grant_map *map)
         return err;
 }
 
-static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
+static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
 {
         int i, err = 0;
 
@@ -301,7 +301,6 @@ static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
                 }
         }
 
-        pr_debug("map %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
         err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, pages);
         if (err)
                 return err;
@@ -314,6 +313,36 @@ static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
         return err;
 }
 
+static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
+{
+        int range, err = 0;
+
+        pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
+
+        /* It is possible the requested range will have a "hole" where we
+         * already unmapped some of the grants. Only unmap valid ranges.
+         */
+        while (pages && !err) {
+                while (pages && !map->unmap_ops[offset].handle) {
+                        offset++;
+                        pages--;
+                }
+                range = 0;
+                while (range < pages) {
+                        if (!map->unmap_ops[offset+range].handle) {
+                                range--;
+                                break;
+                        }
+                        range++;
+                }
+                err = __unmap_grant_pages(map, offset, range);
+                offset += range;
+                pages -= range;
+        }
+
+        return err;
+}
+
 /* ------------------------------------------------------------------ */
 
 static void gntdev_vma_close(struct vm_area_struct *vma)