[PATCH] x86/p2m: fix xenmem_add_to_physmap_one double page removal

[Roger Pau Monne]

If the new gfn matches the previous one (ie: gfn == old_gpfn)
xenmem_add_to_physmap_one will issue a duplicated call to
guest_physmap_remove_page with the same gfn, because the
get_gpfn_from_mfn call has been moved by commit f8582da041 to be
performed before the original page is removed. This leads to the
second guest_physmap_remove_page failing, which was not the case
before commit f8582da041.

Fix this by adding a check that prevents a second call to
guest_physmap_remove_page if the previous one has already removed the
backing page from that gfn.

Fixes: f8582da041 ('x86/mm: pull a sanity check earlier in 
xenmem_add_to_physmap_one()')
Signed-off-by: Roger Pau Monné <roger....@citrix.com>
---
 xen/arch/x86/mm/p2m.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 674a6f4fe9..2bd4d37286 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2813,7 +2813,7 @@ int xenmem_add_to_physmap_one(
     }
 
     /* Unmap from old location, if any. */
-    if ( !rc && old_gpfn != INVALID_M2P_ENTRY )
+    if ( !rc && old_gpfn != INVALID_M2P_ENTRY && !gfn_eq(_gfn(old_gpfn), gpfn) 
)
         rc = guest_physmap_remove_page(d, _gfn(old_gpfn), mfn, PAGE_ORDER_4K);
 
     /* Map at new location. */
-- 
2.33.0