xen/gntdev: remove erronous use of copy_to_user

Since there is now a mapping of granted pages in kernel address space in
both PV and HVM, use it for UNMAP_NOTIFY_CLEAR_BYTE instead of accessing
memory via copy_to_user and triggering sleep-in-atomic warnings.

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

1 files changed, 3 insertions, 10 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 9be3e5e46d1f..3c8803feba26 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -312,17 +312,10 @@ 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 && use_ptemod) {
-                        void __user *tmp = (void __user *)
-                                map->vma->vm_start + map->notify.addr;
-                        err = copy_to_user(tmp, &err, 1);
-                        if (err)
-                                return -EFAULT;
-                        map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
-                } else if (pgno >= offset && pgno < offset + pages) {
-                        uint8_t *tmp = kmap(map->pages[pgno]);
+                if (pgno >= offset && pgno < offset + pages) {
+                        /* No need for kmap, pages are in lowmem */
+                        uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
                         tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
-                        kunmap(map->pages[pgno]);
                         map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
                 }
         }