1 files changed, 22 insertions, 7 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 195707060493..c61934fbf22a 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -81,6 +81,7 @@ static inline int phys_to_machine_mapping_valid(unsigned long pfn)
 static inline unsigned long mfn_to_pfn(unsigned long mfn)
 {
         unsigned long pfn;
+        int ret = 0;
 
         if (xen_feature(XENFEAT_auto_translated_physmap))
                 return mfn;
@@ -95,15 +96,29 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
          * In such cases it doesn't matter what we return (we return garbage),
          * but we must handle the fault without crashing!
          */
-        __get_user(pfn, &machine_to_phys_mapping[mfn]);
+        ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
 try_override:
-        /*
-         * If this appears to be a foreign mfn (because the pfn
-         * doesn't map back to the mfn), then check the local override
-         * table to see if there's a better pfn to use.
+        /* ret might be < 0 if there are no entries in the m2p for mfn */
+        if (ret < 0)
+                pfn = ~0;
+        else if (get_phys_to_machine(pfn) != mfn)
+                /*
+                 * If this appears to be a foreign mfn (because the pfn
+                 * doesn't map back to the mfn), then check the local override
+                 * table to see if there's a better pfn to use.
+                 *
+                 * m2p_find_override_pfn returns ~0 if it doesn't find anything.
+                 */
+                pfn = m2p_find_override_pfn(mfn, ~0);
+
+        /* 
+         * pfn is ~0 if there are no entries in the m2p for mfn or if the
+         * entry doesn't map back to the mfn and m2p_override doesn't have a
+         * valid entry for it.
          */
-        if (get_phys_to_machine(pfn) != mfn)
-                pfn = m2p_find_override_pfn(mfn, pfn);
+        if (pfn == ~0 &&
+                        get_phys_to_machine(mfn) == IDENTITY_FRAME(mfn))
+                pfn = mfn;
 
         return pfn;
 }