x86/p2m: fix xenmem_add_to_physmap_one double page removal

If the new gfn matches the previous one (ie: gpfn == old_gpfn)
xenmem_add_to_physmap_one will issue a duplicated call to
guest_physmap_remove_page with the same guest frame number, 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.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 674a6f4fe9e44f39583a3680f476f0553d815436..2bd4d372869a69343cff390e7f0ab8193c4ecfb4 100644 (file)
--- 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. */