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

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Date:	Tue, 27 Apr 2010 12:13:48 +0200
From:	Andreas Herrmann <herrmann.der.user@...glemail.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] x86, amd: Check X86_FEATURE_OSVW bit before accessing OSVW
 MSRs

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.

Cc: <stable@...nel.org> # .32.x .33.x
Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
---
 arch/x86/kernel/process.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 28ad9f4..0415c3e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -546,11 +546,13 @@ static int __cpuinit check_c1e_idle(const struct cpuinfo_x86 *c)
 		 * 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;
 	}
-- 
1.6.4.4

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