[4.2.y-ckt stable] Patch "KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From f9720de51aeacd81dbb6d4ff9893d35d6d889fd5 Mon Sep 17 00:00:00 2001
From: Haozhong Zhang <haozhong.zhang at intel.com>
Date: Mon, 14 Dec 2015 23:13:38 +0800
Subject: KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX

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 at intel.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
Backported-by: Thomas Lamprecht <t.lamprecht at proxmox.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.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