[PATCH 2/2] [PATCH] disable kvm clock unless addr's LSB is set.

[Glauber Costa <gcosta@redhat.com>]

Use LSB of the address passed through the msr to enable/disable
the clock. Setting it to 1 enables it, setting it to 0 disables it.

As the guest data structures are aligned anyway, this
won't be a problem, as this bit is free.

Guest is changed accordingly

Signed-off-by: Glauber Costa <gcosta@redhat.com>
---
 arch/x86/kernel/kvmclock.c |    2 +-
 arch/x86/kvm/x86.c         |    9 ++++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 7c481a3..f654a12 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -125,7 +125,7 @@ static int kvm_register_clock(void)
 {
 	int cpu = smp_processor_id();
 	int low, high;
-	low = (int)__pa(&per_cpu(hv_clock, cpu));
+	low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1;
 	high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
 
 	return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6abd784..64beff6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -591,8 +591,15 @@ int kvm_set_msr_common(struct kvm_vcpu *
 		if (vcpu->arch.time_page)
 			kvm_release_page_dirty(vcpu->arch.time_page);
 
+		/* we verify if the enable bit is set... */
+		if (!(data & 1)) {
+			vcpu->arch.time = NULL;
+			break;
+		}
+
 		vcpu->arch.time = data & PAGE_MASK;
-		vcpu->arch.time_offset = data & ~PAGE_MASK;
+		/* ...but clean it before doing the actual write */
+		vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
 
 		vcpu->arch.hv_clock.tsc_to_system_mul =
 					clocksource_khz2mult(tsc_khz, 22);
-- 
1.4.2


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