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xen/m2p: use GNTTABOP_unmap_and_replace to reinstate the original mapping

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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
This commit is contained in:
Stefano Stabellini
2013-07-23 17:23:54 +00:00
committed by Konrad Rzeszutek Wilk
parent 072b2064b8
commit ee0726407f
2 changed files with 17 additions and 15 deletions
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11
drivers/xen/gntdev.c
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@@ -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);
}