[PATCH] xen: set P2M entry to INVALID_P2M_ENTRY for ballooned out pages

[Wei Liu <wei.liu2@citrix.com>]

In commit cd9151e2: xen/balloon: set a mapping for ballooned out pages
we have the ballooned out page's mapping set to a scratch page. That commit
also set the P2M entry of ballooned out page to the scratch, which is
not necessary. That triggers BUG_ONs in __set_phys_to_machine when the
page is ballooned in again.

We only need to ensure that the ballooned out pages have valid mapping.
P2M entries of those pages should still be set to INVALID_P2M_ENTRY.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 drivers/xen/balloon.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index a3dc75d..b1a37f3 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -430,8 +430,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	/* No more mappings: invalidate P2M and add to balloon. */
 	for (i = 0; i < nr_pages; i++) {
 		pfn = mfn_to_pfn(frame_list[i]);
-		__set_phys_to_machine(pfn,
-				pfn_to_mfn(page_to_pfn(__get_cpu_var(balloon_scratch_page))));
+		__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 		balloon_append(pfn_to_page(pfn));
 	}
 
-- 
1.7.10.4