linux-kernel - [PATCH] KVM: SVM: fix trashing of MSR_TSC

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Date:	Wed,  6 Jul 2016 15:43:16 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	stable@...r.kernel.org, Borislav Petkov <bp@...en8.de>
Subject: [PATCH] KVM: SVM: fix trashing of MSR_TSC_AUX

I don't know what I was thinking when I wrote commit 46896c73c1a4 ("KVM:
svm: add support for RDTSCP", 2015-11-12); I missed write_rdtscp_aux which
obviously uses MSR_TSC_AUX.

Therefore we do need to save/restore MSR_TSC_AUX in svm_vcpu_run.

Cc: stable@...r.kernel.org
Cc: Borislav Petkov <bp@...en8.de>
Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 16ef31b87452..44f6368f8b45 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -43,6 +43,7 @@
 #include <asm/kvm_para.h>
 
 #include <asm/virtext.h>
+#include <asm/vgtod.h>
 #include "trace.h"
 
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
@@ -1530,9 +1531,6 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 			wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio);
 		}
 	}
-	/* This assumes that the kernel never uses MSR_TSC_AUX */
-	if (static_cpu_has(X86_FEATURE_RDTSCP))
-		wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
 
 	avic_vcpu_load(vcpu, cpu);
 }
@@ -4474,6 +4472,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 	svm->vmcb->save.cr2 = vcpu->arch.cr2;
 
 	clgi();
+	if (static_cpu_has(X86_FEATURE_RDTSCP))
+		wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
 
 	local_irq_enable();
 
@@ -4550,6 +4550,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 		);
 
+	if (static_cpu_has(X86_FEATURE_RDTSCP))
+		wrmsrl(MSR_TSC_AUX, __getcpu());
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
 #else
-- 
1.8.3.1