linux-kernel - [PATCH] KVM: VMX: Fix host initiated access to guest MSR_TSC

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Date:	Mon, 14 Dec 2015 23:13:38 +0800
From:	Haozhong Zhang <haozhong.zhang@...el.com>
To:	kvm@...r.kernel.org
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Haozhong Zhang <haozhong.zhang@...el.com>
Subject: [PATCH] KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX

The current handling of accesses to guest MSR_TSC_AUX returns error if
vcpu does not support rdtscp, though those accesses are initiated by
host. This can result in the reboot failure of some versions of
QEMU. This patch fixes this issue by passing those host initiated
accesses for further handling instead.

Signed-off-by: Haozhong Zhang <haozhong.zhang@...el.com>
---
 arch/x86/kvm/vmx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1a8bfaa..50f2b78 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2802,7 +2802,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = vcpu->arch.ia32_xss;
 		break;
 	case MSR_TSC_AUX:
-		if (!guest_cpuid_has_rdtscp(vcpu))
+		if (!guest_cpuid_has_rdtscp(vcpu) && !msr_info->host_initiated)
 			return 1;
 		/* Otherwise falls through */
 	default:
@@ -2908,7 +2908,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			clear_atomic_switch_msr(vmx, MSR_IA32_XSS);
 		break;
 	case MSR_TSC_AUX:
-		if (!guest_cpuid_has_rdtscp(vcpu))
+		if (!guest_cpuid_has_rdtscp(vcpu) && !msr_info->host_initiated)
 			return 1;
 		/* Check reserved bit, higher 32 bits should be zero */
 		if ((data >> 32) != 0)
-- 
2.6.4

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