xen-gntdev: Fix unmap notify on PV domains

In paravirtualized guests, the struct page* for mappings is only a
placeholder, and cannot be used to access the granted memory. Use the
userspace mapping that we have set up in order to implement
UNMAP_NOTIFY_CLEAR_BYTE.

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

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 2aa83166da32..75f8037c9833 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -289,7 +289,12 @@ static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
 
         if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                 int pgno = (map->notify.addr >> PAGE_SHIFT);
-                if (pgno >= offset && pgno < offset + pages) {
+                if (pgno >= offset && pgno < offset + pages && use_ptemod) {
+                        void __user *tmp;
+                        tmp = map->vma->vm_start + map->notify.addr;
+                        copy_to_user(tmp, &err, 1);
+                        map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
+                } else if (pgno >= offset && pgno < offset + pages) {
                         uint8_t *tmp = kmap(map->pages[pgno]);
                         tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
                         kunmap(map->pages[pgno]);
@@ -298,7 +303,7 @@ 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, pages);
+        err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, pages);
         if (err)
                 return err;