linux-kernel - [29/39] x86, amd: Check X86_FEATURE_OSVW bit before accessing OSVW MSRs

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Date:	Mon, 24 May 2010 16:15:41 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Andreas Herrmann <andreas.herrmann3@....com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [29/39] x86, amd: Check X86_FEATURE_OSVW bit before accessing OSVW MSRs


2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Andreas Herrmann <herrmann.der.user@...glemail.com>

commit f01487119dda3d9f58c9729c7361ecc50a61c188 upstream.

If host CPU is exposed to a guest the OSVW MSRs are not guaranteed
to be present and a GP fault occurs. Thus checking the feature flag is
essential.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
LKML-Reference: <20100427101348.GC4489@...erich.amd.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/kernel/process.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -539,11 +539,13 @@ static int __cpuinit check_c1e_idle(cons
 		 * check OSVW bit for CPUs that are not affected
 		 * by erratum #400
 		 */
-		rdmsrl(MSR_AMD64_OSVW_ID_LENGTH, val);
-		if (val >= 2) {
-			rdmsrl(MSR_AMD64_OSVW_STATUS, val);
-			if (!(val & BIT(1)))
-				goto no_c1e_idle;
+		if (cpu_has(c, X86_FEATURE_OSVW)) {
+			rdmsrl(MSR_AMD64_OSVW_ID_LENGTH, val);
+			if (val >= 2) {
+				rdmsrl(MSR_AMD64_OSVW_STATUS, val);
+				if (!(val & BIT(1)))
+					goto no_c1e_idle;
+			}
 		}
 		return 1;
 	}


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