Re: [Xen-devel] guest being crashed from viridian_start_apic_assist()

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 03 June 2016 15:38
> To: Paul Durrant
> Cc: xen-devel
> Subject: RE: guest being crashed from viridian_start_apic_assist()
> 
> >>> On 03.06.16 at 15:31, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 03 June 2016 14:06
> >>
> >> What I find more problematic looking at those functions (but
> >> unrelated to the problem here afaict) is the
> >> vlapic_virtual_intr_delivery_enabled() related logic and its
> >> interaction with the Viridian APIC assist (leaving aside nested
> >> mode for the moment): vlapic_has_pending_irq() won't do
> >> anything with the APIC assist in that case, but if force_ack is
> >> true in vlapic_ack_pending_irq() there will be an interaction.
> >
> > ...and the interaction would indeed be the crash you saw, I think, because
> > you could start an APIC assist when vlapic_virtual_intr_delivery_enabled()
> is
> > true, but never complete it because vlapic_has_pending_irq() bails before
> > doing so. Thus, attempting the next APIC assist would lead to a
> > domain_crash().
> 
> With one caveat - this was on a Nehalem, which doesn't have that
> capability. Hence me saying "unrelated"...
> 

Ah, I see.

  Paul

> Jan


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