Re: [PATCH 2/2] x86/hvm: fix corrupt ACPI PM-Timer during live migration

[Kouya Shimura <kouya@jp.fujitsu.com>]

On 03/21/2013 07:01 PM, Jan Beulich wrote:
>>>> On 21.03.13 at 08:32, Kouya Shimura <kouya@jp.fujitsu.com> wrote:
>> @@ -244,19 +245,11 @@ static int handle_pmt_io(
>>    static int pmtimer_save(struct domain *d, hvm_domain_context_t *h)
>>    {
>>        PMTState *s = &d->arch.hvm_domain.pl_time.vpmt;
>> -    uint32_t x, msb = s->pm.tmr_val & TMR_VAL_MSB;
>>        int rc;
>>
>>        spin_lock(&s->lock);
>>
>> -    /* Update the counter to the guest's current time.  We always save
>> -     * with the domain paused, so the saved time should be after the
>> -     * last_gtime, but just in case, make sure we only go forwards */
>
> So on the previous patch version (which you said this one is
> identical to) I stated that you lose this property of guaranteeing
> no backward move. Am I right in assuming that patch 1 is now
> supposed to take care of this?

Yes.  Patch 1 guarantees  that the timer counter only goes forwards.

> In any case I'll have to defer to Keir or Tim for that first one.
>
>> -    x = ((s->vcpu->arch.hvm_vcpu.guest_time - s->last_gtime) * s->scale) >> 32;
>> -    if ( x < 1UL<<31 )
>> -        s->pm.tmr_val += x;
>> -    if ( (s->pm.tmr_val & TMR_VAL_MSB) != msb )
>> -        s->pm.pm1a_sts |= TMR_STS;
>> +    pmt_update_time(s, 0);
>
> Here I can only quote part of my previous reply, which I don't
> think you responded to:
>
> "Also, in delay_for_missed_ticks mode you now use a slightly
>   different time for updating s->pm - did you double check that
>   this is not going to be a problem? Or else, the flag above could
>   similarly be used to circumvent this, or hvm_get_guest_time()
>   could be made return the frozen time (I suppose, but didn't
>   verify - as it appears to be an assumption already before your
>   patch -, that pt_freeze_time() runs before pmtimer_save())."
>
> You said you'd think about it, but I don't recall seeing any other
> outcome from that than the two patches, and I can't relate the
> first patch to this aspect.

In patch 1, pmt_update_time() calls the new function hvm_get_base_time()
which returns the frozen time when the vcpu is de-scheduled.
And I confirmed pmtimer_save() is surely called after pt_freeze_time()
from my test and review.
So, if both patches are applied, there is no difference in
delay_for_missed_ticks mode.

Thanks,
Kouya