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

On 03/21/2013 07:01 PM, Jan Beulich wrote:
On 21.03.13 at 08:32, Kouya Shimura <kouya@xxxxxxxxxxxxxx> 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;


-    /* 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.


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