From: David Woodhouse When computing kvmclock and it's currently in master-clock mode, fall back to the non-master-clock path if the clock read fails, e.g. if the kernel's clocksource transitioning away from TSC but ka->use_master_clock hasn't been updated yet. The rdtsc() fallback was added (well, kept) in commit c68dc1b577ea ("KVM: x86: Report host tsc and realtime values in KVM_GET_CLOCK") purely to avoid uninitialized variables and compilation problems on 32-bit kernels (already addressed). In hindsight, keeping the rdtsc() was a hack and a mistake. Link: https://lore.kernel.org/all/CAOQ_QsgVqS_PuJo8F10Gg5Xw+tKt+5gDx+kJf1j3CiPO4MAOqg@mail.gmail.com Signed-off-by: David Woodhouse [sean: isolate from refactoring changes, write changelog] Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index cd2a140e8e63..7768a8909cf8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1674,14 +1674,13 @@ static bool __get_kvmclock_master_clock(struct kvm *kvm, if (!tsc_hz) return false; - if (kvm_get_walltime_and_clockread(&ts, &data->host_tsc)) { - data->realtime = ts.tv_nsec + NSEC_PER_SEC * ts.tv_sec; - data->flags |= KVM_CLOCK_REALTIME | KVM_CLOCK_HOST_TSC; - } else { - data->host_tsc = rdtsc(); - } + if (!kvm_get_walltime_and_clockread(&ts, &data->host_tsc)) + return false; + + data->realtime = ts.tv_nsec + NSEC_PER_SEC * ts.tv_sec; + data->flags |= KVM_CLOCK_REALTIME | KVM_CLOCK_HOST_TSC | + KVM_CLOCK_TSC_STABLE; - data->flags |= KVM_CLOCK_TSC_STABLE; hv_clock.tsc_timestamp = ka->master_cycle_now; hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset; kvm_get_time_scale(NSEC_PER_SEC, tsc_hz, -- 2.55.0.571.g244d577d93-goog