[PATCH] kvm: x86: Update tsc multiplier on change.

[Owen Hofmann <osh@google.com>]

vmx.c writes the TSC_MULTIPLIER field in vmx_vcpu_load, but only when a
vcpu has migrated physical cpus. Record the last value written and
update in vmx_vcpu_load on any change, otherwise a cpu migration must
occur for TSC frequency scaling to take effect.

Fixes: ff2c3a1803775cc72dc6f624b59554956396b0ee
Signed-off-by: Owen Hofmann <osh@google.com>
---
 arch/x86/kvm/vmx.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e2951b6..0ff4537 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -596,6 +596,8 @@ struct vcpu_vmx {
 	/* Support for PML */
 #define PML_ENTITY_NUM		512
 	struct page *pml_pg;
+
+	u64 current_tsc_ratio;
 };
 
 enum segment_cache_field {
@@ -2127,14 +2129,16 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
 		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
 
-		/* Setup TSC multiplier */
-		if (cpu_has_vmx_tsc_scaling())
-			vmcs_write64(TSC_MULTIPLIER,
-				     vcpu->arch.tsc_scaling_ratio);
-
 		vmx->loaded_vmcs->cpu = cpu;
 	}
 
+	/* Setup TSC multiplier */
+	if (kvm_has_tsc_control &&
+	    vmx->current_tsc_ratio != vcpu->arch.tsc_scaling_ratio) {
+		vmx->current_tsc_ratio = vcpu->arch.tsc_scaling_ratio;
+		vmcs_write64(TSC_MULTIPLIER, vmx->current_tsc_ratio);
+	}
+
 	vmx_vcpu_pi_load(vcpu, cpu);
 }
 
-- 
2.7.0.rc3.207.g0ac5344