[3.8.y.z extended stable] Patch "kvm: x86: fix apic_base enable check" has been added to staging queue

[Kamal Mostafa]

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

    kvm: x86: fix apic_base enable check

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.19.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 3876db68add3d93ba3777c3b5f9e730e88040a65 Mon Sep 17 00:00:00 2001
From: Andrew Jones <drjones at redhat.com>
Date: Wed, 15 Jan 2014 13:39:59 +0100
Subject: kvm: x86: fix apic_base enable check

commit 0dce7cd67fd9055c4a2ff278f8af1431e646d346 upstream.

Commit e66d2ae7c67bd moved the assignment
vcpu->arch.apic_base = value above a condition with
(vcpu->arch.apic_base ^ value), causing that check
to always fail. Use old_value, vcpu->arch.apic_base's
old value, in the condition instead.

Signed-off-by: Andrew Jones <drjones at redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
[ kamal: backport to 3.8 (collect old_value) ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kvm/lapic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 6e27290..e77b0f4 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1289,6 +1289,7 @@ u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu)

 void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 {
+	u64 old_value = vcpu->arch.apic_base;
 	struct kvm_lapic *apic = vcpu->arch.apic;

 	if (!apic) {
@@ -1302,7 +1303,7 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 	vcpu->arch.apic_base = value;

 	/* update jump label if enable bit changes */
-	if ((vcpu->arch.apic_base ^ value) & MSR_IA32_APICBASE_ENABLE) {
+	if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE) {
 		if (value & MSR_IA32_APICBASE_ENABLE)
 			static_key_slow_dec_deferred(&apic_hw_disabled);
 		else
--
1.8.3.2