KVM: SVM: Adjust tsc_offset only if tsc_unstable

The tsc_offset adjustment in svm_vcpu_load is executed
unconditionally even if Linux considers the host tsc as
stable. This causes a Linux guest detecting an unstable tsc
in any case.
This patch removes the tsc_offset adjustment if the host tsc
is stable. The guest will now get the benefit of a stable
tsc too.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 10 insertions, 8 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7f4e225feebf..b373ae6fb974 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -765,14 +765,16 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
         if (unlikely(cpu != vcpu->cpu)) {
                 u64 delta;
 
-                /*
-                 * Make sure that the guest sees a monotonically
-                 * increasing TSC.
-                 */
-                delta = vcpu->arch.host_tsc - native_read_tsc();
-                svm->vmcb->control.tsc_offset += delta;
-                if (is_nested(svm))
-                        svm->nested.hsave->control.tsc_offset += delta;
+                if (check_tsc_unstable()) {
+                        /*
+                         * Make sure that the guest sees a monotonically
+                         * increasing TSC.
+                         */
+                        delta = vcpu->arch.host_tsc - native_read_tsc();
+                        svm->vmcb->control.tsc_offset += delta;
+                        if (is_nested(svm))
+                                svm->nested.hsave->control.tsc_offset += delta;
+                }
                 vcpu->cpu = cpu;
                 kvm_migrate_timers(vcpu);
                 svm->asid_generation = 0;