[PATCH v2] KVM: x86: update masterclock values on TSC writes

Marcelo Tosatti
2014-11-04T23:30:59Z

When the guest writes to the TSC, the masterclock TSC copy must be
updated as well along with the TSC_OFFSET update, otherwise a negative
tsc_timestamp is calculated at kvm_guest_time_update.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0033df3..50b6f56 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1237,21 +1237,21 @@ void kvm_track_tsc_matching(struct kvm_vcpu *vcpu)
{
#ifdef CONFIG_X86_64
bool vcpus_matched;
- bool do_request = false;
struct kvm_arch *ka = &vcpu->kvm->arch;
struct pvclock_gtod_data *gtod = &pvclock_gtod_data;

vcpus_matched = (ka->nr_vcpus_matched_tsc + 1 ==
atomic_read(&vcpu->kvm->online_vcpus));

- if (vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC)
- if (!ka->use_master_clock)
- do_request = 1;
-
- if (!vcpus_matched && ka->use_master_clock)
- do_request = 1;
-
- if (do_request)
+ /*
+ * If the vcpus have matched TSCs and host clocksource is TSC,
+ * perform request to enable masterclock.
+ *
+ * If the masterclock is enabled, perform request to update
+ * masterclock values.
+ */
+ if ((vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC) ||
+ ka->use_master_clock)
kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);

trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc,