2017-01-20 13:00-0200, Marcelo Tosatti:
> On Fri, Jan 20, 2017 at 03:12:56PM +0100, Radim Krcmar wrote:
>> 2017-01-20 10:20-0200, Marcelo Tosatti:
>> > + do {
>> > + /*
>> > + * We are measuring the delay between
>> > + * kvm_hypercall and rdtsc using TSC,
>> > + * and converting that delta to
>> > + * tsc_to_system_mul and tsc_shift
>> > + * So any changes to tsc_to_system_mul
>> > + * and tsc_shift in this region
>> > + * invalidate the measurement.
>> > + */
>> > + version = pvclock_read_begin(src);
>> > +
>> > + ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING,
>> > + clock_off_gpa,
>> > + KVM_CLOCK_PAIRING_WALLCLOCK);
>> > + if (ret != 0) {
>> > + pr_err("clock offset hypercall ret %lu\n", ret);
>> > + spin_unlock(&kvm_ptp_lock);
>> > + preempt_enable_notrace();
>> > + return -EOPNOTSUPP;
>> > + }
>> > +
>> > + tspec.tv_sec = clock_off.sec;
>> > + tspec.tv_nsec = clock_off.nsec;
>> > + ret = __pvclock_read_cycles(src, clock_off.tsc);
>> > + flags = src->flags;
>> > + } while (pvclock_read_retry(src, version));
>> > +
>> > + preempt_enable_notrace();
>> > +
>> > + system_counter->cycles = ret;
>> > + system_counter->cs = get_kvmclock_cs();
>>
>> Can't we use clocksource_tsc and just pass the tsc without kvmclock in
>> the middle?
>
> No, it has to be the kvmclock value.
What happens if the guest switches from kvmclock to tsc?
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