xen/gntdev: safely unmap grants in case they are still in use

Use gnttab_unmap_refs_async() to wait until the mapped pages are no
longer in use before unmapping them.

This allows userspace programs to safely use Direct I/O and AIO to a
network filesystem which may retain refs to pages in queued skbs after
the filesystem I/O has completed.

Signed-off-by: Jennifer Herbert <jennifer.herbert@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 31 insertions, 5 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 3c2534433b30..bccc54a80559 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -309,9 +309,30 @@ static int map_grant_pages(struct grant_map *map)
         return err;
 }
 
+struct unmap_grant_pages_callback_data
+{
+        struct completion completion;
+        int result;
+};
+
+static void unmap_grant_callback(int result,
+                                 struct gntab_unmap_queue_data *data)
+{
+        struct unmap_grant_pages_callback_data* d = data->data;
+
+        d->result = result;
+        complete(&d->completion);
+}
+
 static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
 {
         int i, err = 0;
+        struct gntab_unmap_queue_data unmap_data;
+        struct unmap_grant_pages_callback_data data;
+
+        init_completion(&data.completion);
+        unmap_data.data = &data;
+        unmap_data.done= &unmap_grant_callback;
 
         if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                 int pgno = (map->notify.addr >> PAGE_SHIFT);
@@ -323,11 +344,16 @@ static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
                 }
         }
 
-        err = gnttab_unmap_refs(map->unmap_ops + offset,
-                        use_ptemod ? map->kunmap_ops + offset : NULL, map->pages + offset,
-                        pages);
-        if (err)
-                return err;
+        unmap_data.unmap_ops = map->unmap_ops + offset;
+        unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
+        unmap_data.pages = map->pages + offset;
+        unmap_data.count = pages;
+
+        gnttab_unmap_refs_async(&unmap_data);
+
+        wait_for_completion(&data.completion);
+        if (data.result)
+                return data.result;
 
         for (i = 0; i < pages; i++) {
                 if (map->unmap_ops[offset+i].status)