xen/m2p: use GNTTABOP_unmap_and_replace to reinstate the original mapping

GNTTABOP_unmap_grant_ref unmaps a grant and replaces it with a 0
mapping instead of reinstating the original mapping.
Doing so separately would be racy.

To unmap a grant and reinstate the original mapping atomically we use
GNTTABOP_unmap_and_replace.
GNTTABOP_unmap_and_replace doesn't work with GNTMAP_contains_pte, so
don't use it for kmaps.  GNTTABOP_unmap_and_replace zeroes the mapping
passed in new_addr so we have to reinstate it, however that is a
per-cpu mapping only used for balloon scratch pages, so we can be sure that
it's not going to be accessed while the mapping is not valid.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: alex@alex.org.uk
CC: dcrisan@flexiant.com

[v1: Konrad fixed up the conflicts]
Conflicts:
	arch/x86/xen/p2m.c

1 files changed, 2 insertions, 9 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index eab5427c75f5..e41c79c986ea 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -272,19 +272,12 @@ static int map_grant_pages(struct grant_map *map)
                  * with find_grant_ptes.
                  */
                 for (i = 0; i < map->count; i++) {
-                        unsigned level;
                         unsigned long address = (unsigned long)
                                 pfn_to_kaddr(page_to_pfn(map->pages[i]));
-                        pte_t *ptep;
-                        u64 pte_maddr = 0;
                         BUG_ON(PageHighMem(map->pages[i]));
 
-                        ptep = lookup_address(address, &level);
-                        pte_maddr = arbitrary_virt_to_machine(ptep).maddr;
-                        gnttab_set_map_op(&map->kmap_ops[i], pte_maddr,
-                                map->flags |
-                                GNTMAP_host_map |
-                                GNTMAP_contains_pte,
+                        gnttab_set_map_op(&map->kmap_ops[i], address,
+                                map->flags | GNTMAP_host_map,
                                 map->grants[i].ref,
                                 map->grants[i].domid);
                 }