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>
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7f4e225..b373ae6 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -765,14 +765,16 @@
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;