On Thu, Oct 10, 2019 at 7:55 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 10/10/19 09:30, Suleiman Souhlal wrote:
> > +kvm_hostclock_enable(struct clocksource *cs)
> > +{
> > + pv_timekeeper_enabled = 1;
> > +
> > + old_vclock_mode = kvm_clock.archdata.vclock_mode;
> > + kvm_clock.archdata.vclock_mode = VCLOCK_TSC;
> > + return 0;
> > +}
> > +
> > +static void
> > +kvm_hostclock_disable(struct clocksource *cs)
> > +{
> > + pv_timekeeper_enabled = 0;
> > + kvm_clock.archdata.vclock_mode = old_vclock_mode;
> > +}
> > +
>
> Why do you poke at kvm_clock? Instead you should add
>
> .archdata = { .vclock_mode = VCLOCK_TSC },
>
> to the kvm_hostclock declaration.
Yeah, what I was doing does not make sense.
> Please also check that the invariant TSC CPUID bit
> CPUID[0x80000007].EDX[8] is set before enabling this feature.
Will do.
>
> Paolo
>
> > + pvtk = &pv_timekeeper;
> > + do {
> > + gen = pvtk_read_begin(pvtk);
> > + if (!(pv_timekeeper.flags & PVCLOCK_TIMEKEEPER_ENABLED))
> > + return;
> > +
> > + pvclock_copy_into_read_base(pvtk, &tk->tkr_mono,
> > + &pvtk->tkr_mono);
> > + pvclock_copy_into_read_base(pvtk, &tk->tkr_raw, &pvtk->tkr_raw);
> > +
> > + tk->xtime_sec = pvtk->xtime_sec;
> > + tk->ktime_sec = pvtk->ktime_sec;
> > + tk->wall_to_monotonic.tv_sec = pvtk->wall_to_monotonic_sec;
> > + tk->wall_to_monotonic.tv_nsec = pvtk->wall_to_monotonic_nsec;
> > + tk->offs_real = pvtk->offs_real;
> > + tk->offs_boot = pvtk->offs_boot;
> > + tk->offs_tai = pvtk->offs_tai;
> > + tk->raw_sec = pvtk->raw_sec;
> > + } while (pvtk_read_retry(pvtk, gen));
> > +}
> > +
>
> Should you write an "enabled value" (basically the flags) into pvtk as well?
I think we have that already (pvtk->flags).
I'll change the if statement above to use pvtk instead of pv_timekeeper.
> > +kvm_hostclock_init(void)
> > +{
> > + unsigned long pa;
> > +
> > + pa = __pa(&pv_timekeeper);
> > + wrmsrl(MSR_KVM_TIMEKEEPER_EN, pa);
>
>
> As Vitaly said, a new CPUID bit must be defined in
> Documentation/virt/kvm/cpuid.txt, and used here. Also please make bit 0
> an enable bit.
I think I might not be able to move the enable bit to 0 because we
need the generation count (pvclock_timekeeper.gen) to be the first
word of the struct due to the way we copy the data to userspace,
similarly to how kvm_setup_pvclock_page() does it.
I also noticed the comment in kvm_copy_into_pvtk() references the
wrong function, which I will fix in the next revision.
Thanks for the feedback.
-- Suleiman
