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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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21
arch/x86/xen/p2m.c
View file

@ -161,6 +161,7 @@
#include <asm/xen/page.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
#include <xen/balloon.h>
#include <xen/grant_table.h>
#include "multicalls.h"
@ -967,7 +968,10 @@ int m2p_remove_override(struct page *page,
if (kmap_op != NULL) {
if (!PageHighMem(page)) {
struct multicall_space mcs;
struct gnttab_unmap_grant_ref *unmap_op;
struct gnttab_unmap_and_replace *unmap_op;
struct page *scratch_page = get_balloon_scratch_page();
unsigned long scratch_page_address = (unsigned long)
__va(page_to_pfn(scratch_page) << PAGE_SHIFT);
/*
* It might be that we queued all the m2p grant table
@ -990,20 +994,25 @@ int m2p_remove_override(struct page *page,
}
mcs = xen_mc_entry(
sizeof(struct gnttab_unmap_grant_ref));
sizeof(struct gnttab_unmap_and_replace));
unmap_op = mcs.args;
unmap_op->host_addr = kmap_op->host_addr;
unmap_op->new_addr = scratch_page_address;
unmap_op->handle = kmap_op->handle;
unmap_op->dev_bus_addr = 0;
MULTI_grant_table_op(mcs.mc,
GNTTABOP_unmap_grant_ref, unmap_op, 1);
GNTTABOP_unmap_and_replace, unmap_op, 1);
xen_mc_issue(PARAVIRT_LAZY_MMU);
set_pte_at(&init_mm, address, ptep,
pfn_pte(pfn, PAGE_KERNEL));
mcs = __xen_mc_entry(0);
MULTI_update_va_mapping(mcs.mc, scratch_page_address,
pfn_pte(page_to_pfn(get_balloon_scratch_page()),
PAGE_KERNEL_RO), 0);
xen_mc_issue(PARAVIRT_LAZY_MMU);
kmap_op->host_addr = 0;
put_balloon_scratch_page();
}
}

11
drivers/xen/gntdev.c
View file

@ -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);
}