KVM: x86: update masterclock values on TSC writes

commit 7f187922ddf6b67f2999a76dcb71663097b75497 upstream.

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.

Once "if (!vcpus_matched && ka->use_master_clock)" is simplified to
"if (ka->use_master_clock)", the corresponding "if (!ka->use_master_clock)"
becomes redundant, so remove the do_request boolean and collapse
everything into a single condition.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index adfc30d9f9f4beb136693c9111486ef22415dbde..41ba726c1ce21f1d03a16f8ba7cefad9e621cc13 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1182,21 +1182,22 @@ 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)
+       /*
+        * Once the masterclock is enabled, always perform request in
+        * order to update it.
+        *
+        * In order to enable masterclock, the host clocksource must be TSC
+        * and the vcpus need to have matched TSCs.  When that happens,
+        * perform request to enable masterclock.
+        */
+       if (ka->use_master_clock ||
+           (gtod->clock.vclock_mode == VCLOCK_TSC && vcpus_matched))
                kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
 
        trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc,