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 <mtosatti@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 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?
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