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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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"...

Jan


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