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 | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1ba08278a9a9..c4b07d6f7bf1 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1620,6 +1620,11 @@ static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now) return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC; } +#else +static inline bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now) +{ + return false; +} #endif /* @@ -1724,18 +1729,18 @@ 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; - } + if (!ka->use_master_clock) + 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; + 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()); } u64 get_kvmclock_ns(struct kvm *kvm) -- 1.8.3.1
