kvm: x86: Update tsc multiplier on change.

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.

Cc: stable@vger.kernel.org
Fixes: ff2c3a1803775cc72dc6f624b59554956396b0ee
Signed-off-by: Owen Hofmann <osh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e2951b6edbbc..0ff453749a90 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);
 }