linux-kernel - [PATCH 4.2.y-ckt 014/273] KVM: VMX: Fix host initiated access to guest MSR_TSC

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Date:	Mon,  7 Mar 2016 14:46:45 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Haozhong Zhang <haozhong.zhang@...el.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 014/273] KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Haozhong Zhang <haozhong.zhang@...el.com>

commit 81b1b9ca6d5ca5f3ce91c0095402def657cf5db3 upstream.

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>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Backported-by: Thomas Lamprecht <t.lamprecht@...xmox.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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 9906a08..8db7c2f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2673,7 +2673,7 @@ 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 (!to_vmx(vcpu)->rdtscp_enabled)
+		if (!to_vmx(vcpu)->rdtscp_enabled && !msr_info->host_initiated)
 			return 1;
 		/* Otherwise falls through */
 	default:
@@ -2779,7 +2779,7 @@ 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 (!vmx->rdtscp_enabled)
+		if (!vmx->rdtscp_enabled && !msr_info->host_initiated)
 			return 1;
 		/* Check reserved bit, higher 32 bits should be zero */
 		if ((data >> 32) != 0)
-- 
2.7.0