linux-kernel - [PATCH 11/11] xen/m2p: Check whether the MFN has IDENTITY

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Date:	Mon, 31 Jan 2011 17:44:36 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	linux-kernel@...r.kernel.org, Xen-devel@...ts.xensource.com,
	konrad@...nel.org, jeremy@...p.org
Cc:	hpa@...or.com, stefano.stabellini@...citrix.com,
	Ian.Campbell@...citrix.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [PATCH 11/11] xen/m2p: Check whether the MFN has IDENTITY_FRAME bit set..

From: Stefano Stabellini <stefano.stabellini@...citrix.com>

If we have the IDENTITY_FRAME bit set from the P2M, there
is no point in looking up MFN in the M2P override. This is
b/c the MFN is a physical MFN.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 arch/x86/include/asm/xen/page.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index ed46ec2..e6f7f37 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;
+	unsigned long p2m_mfn;
 
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return mfn;
@@ -102,7 +103,12 @@ try_override:
 	 * doesn't map back to the mfn), then check the local override
 	 * table to see if there's a better pfn to use.
 	 */
-	if (get_phys_to_machine(pfn) != mfn)
+	p2m_mfn = get_phys_to_machine(pfn);
+
+	if (p2m_mfn == IDENTITY_FRAME(mfn))
+		return pfn;
+
+	if (p2m_mfn != mfn)
 		pfn = m2p_find_override_pfn(mfn, pfn);
 
 	return pfn;
-- 
1.7.1

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