Re: [Xen-devel] [PATCH] x86/hvm: implement save/restore for posted interrupts

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Andrew Cooper
> Sent: Friday, September 19, 2014 10:52 AM
> 
> On 19/09/2014 14:39, Jan Beulich wrote:
> >>>> On 19.09.14 at 15:32, <olaf@xxxxxxxxx> wrote:
> >> On Thu, Sep 18, Zhang, Yang Z wrote:
> >>
> >>> Zhang, Yang Z wrote on 2014-09-01:
> >>>> Zhang, Yang Z wrote on 2014-08-08:
> >>>>> Can you tell how you reproduce it? I am following the steps you told
> >>>>> me previously, but I cannot reproduce it with this fixing.
> >>>> Any update on this?
> >>> Ping again.
> >> I will have a look at this issue next week.
> > Btw., Andrew Cooper hinted at the possibility of this series
> >
> > http://lists.xenproject.org/archives/html/xen-devel/2014-09/msg02753.html
> >
> > (particularly patch 2) having an effect on migration problems
> > between APICV-capable and -incapable systems, i.e. perhaps
> > worth a try in this context too.
> >
> > Jan
> 
> The issue XenServer observes is that problems occur even when migrating
> between two identical machines, one with APICV enabled, and one disabled.
> 
> Given the now-discovered issues with Xen's x2apic handling, it is
> entirely possible that the differences between the emulated and real
> APICs was enough to cause issues.   And yet, it could be a mixture of
> all of the issues identified so far.
> 

Have to say I didn't see any explicit message that this issue is related to 
two machines with different capabilities (one with APICv enabled, and
one disabled).

by reading original commit message:
----
Saving and restoring a PVonHVM guest on a host which has the VMX
"Posted Interrupt Processing" feature enabled will fail because the
xen-platform-pci device does not receive interrupts anymore after
restore. The reason is that the IRQs are not maintained in APIC_IRR,
but in a separate PIR array. This info is lost during the save
operation.
----

I really thought it's related to migration between two machines which
both have APICv enabled. Not sure whether Yang realized this point.

Thanks
Kevin

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