On 17/11/2016 12:38, Marcelo Tosatti wrote: > On Wed, Nov 16, 2016 at 06:31:30PM +0100, Paolo Bonzini wrote: >> Going through the first VCPU is wrong if you follow a KVM_SET_CLOCK with >> a KVM_GET_CLOCK immediately after, without letting the VCPU run and >> call kvm_guest_time_update. >> >> To fix this, compute the kvmclock value ourselves, using the master >> clock (tsc, nsec) pair as the base and the host CPU frequency as >> the scale. >> >> Reported-by: Marcelo Tosatti <[email protected]> >> Signed-off-by: Paolo Bonzini <[email protected]> >> --- >> arch/x86/kvm/x86.c | 21 +++++++++++++-------- >> 1 file changed, 13 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 1ba08278a9a9..bd138a79404a 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1724,18 +1724,23 @@ static void kvm_gen_update_masterclock(struct kvm >> *kvm) >> >> static u64 __get_kvmclock_ns(struct kvm *kvm) >> { >> - struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, 0); >> struct kvm_arch *ka = &kvm->arch; >> - s64 ns; >> + struct pvclock_vcpu_time_info hv_clock; >> >> - if (vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) { >> - u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc()); >> - ns = __pvclock_read_cycles(&vcpu->arch.hv_clock, tsc); >> - } else { >> - ns = ktime_get_boot_ns() + ka->kvmclock_offset; >> + spin_lock(&ka->pvclock_gtod_sync_lock); >> + if (!ka->use_master_clock) { >> + spin_unlock(&ka->pvclock_gtod_sync_lock); >> + return ktime_get_boot_ns() + ka->kvmclock_offset; >> } >> >> - return ns; >> + hv_clock.tsc_timestamp = ka->master_cycle_now; >> + hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset; >> + spin_unlock(&ka->pvclock_gtod_sync_lock); >> + >> + kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL, >> + &hv_clock.tsc_shift, >> + &hv_clock.tsc_to_system_mul); >> + return __pvclock_read_cycles(&hv_clock, rdtsc()); >> } > > Missing TSC scaling? > > /* With all the info we got, fill in the values */ > > if (kvm_has_tsc_control) > tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz); > > Should use kvm_read_l1_tsc to convert as well?
We don't have a vcpu, so we cannot use either kvm_scale_tsc or kvm_read_l1_tsc. But luckily it's not necessary here, because we're using cpu_tsc_khz and rdtsc. Paolo
