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Re: [Xen-devel] Interrupt injection with ISR set on Intel hardware
- To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, 'Jan Beulich' <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 1 Nov 2018 09:18:14 +0000
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 01 Nov 2018 09:18:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 01/11/2018 00:40, Tian, Kevin wrote:
>> From: Tian, Kevin
>> Sent: Tuesday, October 30, 2018 3:00 PM
>>
>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>>> Sent: Thursday, October 25, 2018 9:58 PM
>>>
>>>>>> On 25.10.18 at 15:02, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> On 25/10/18 13:51, Jan Beulich wrote:
>>>>>>>> On 15.10.18 at 14:06, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>>> From the debugging, we see that PPR/IRR/ISR appear to retain their
>>> state
>>>>>> across the mwait, and there is nothing in the manual which I can see
>>>>>> discussing the interaction of LAPIC state and C states.
>>>>> Is it perhaps a bad idea to go idle with an un-acked interrupt?
>>>> Most likely.
>>>>
>>>> Then again, going idle with an un-acked line interrupt does appear to
>>>> work. It is only un-acked edge interrupts which appear to hit this issue.
>>> Well, non-maskable MSI are the only ones (outside of "new" IO-APIC
>>> ack mode, which should not be used on recent hardware because of
>>> directed EOI presumably being available everywhere) where the ack
>>> gets deferred until the .end hook (i.e. after the handler was run).
>>> IOW AFAICT line interrupts would never be pending when we go idle.
>>>
>>>> Still - I'd prefer some guidance from the hardware folk as to what can
>>>> realistically be expected here.
>>> Fully agree.
>> Just sent a mail internally to get clarification.
>>
> One question.
>
> in the first mail, Roger mentioned:
> --
> The issue is caused by what seems to be an interrupt injection while
> Xen is still servicing a previous interrupt (ie: the interrupt hasn't
> been EOI'ed and ISR for the vector is set) with **the same or lower
> priority** than the interrupt currently being serviced.
> --
>
> from the debug log, it's actually the exact same vector (0x21) as
> what is being in service in peoi stack.
Yes - the problem is a repeat delivery of an interrupt which Xen thinks
it is already in the middle of processing.
>
> Do you actually see the scenario "with the same or lower priority"?
> If yes, can you post the debug log too?
I'm afraid that I don't understand the question. A repeat delivery of
vector 0x21 is the same priority.
I haven't seen an example of a lower priority interrupt being accepted,
but that might just be down to the repro scenario. Unfortunately, XTF
isn't usable on native hardware yet so I can't experiment cleanly in
this area.
~Andrew
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