From 388138782b622269194d1693ab244f59aaa3fbaf Mon Sep 17 00:00:00 2001
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Date: Wed, 2 Feb 2011 18:32:59 +0000
Subject: [PATCH] --- yaml --- r: 234174 b: refs/heads/master c:
 706cc9d2a4cb9b03217e15b0bb3d117f4d5109ee h: refs/heads/master v: v3

---
 [refs]                                |  2 +-
 trunk/arch/x86/include/asm/xen/page.h | 29 ++++++++++++++++++++-------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/[refs] b/[refs]
index 9261f88475ac..7d5a4270e5fa 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 146c4e511717e581065800938537b276173d8548
+refs/heads/master: 706cc9d2a4cb9b03217e15b0bb3d117f4d5109ee
diff --git a/trunk/arch/x86/include/asm/xen/page.h b/trunk/arch/x86/include/asm/xen/page.h
index 195707060493..c61934fbf22a 100644
--- a/trunk/arch/x86/include/asm/xen/page.h
+++ b/trunk/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;
 }