Re: [PATCH v3] enable x2APIC without interrupt remapping under KVM

[ebiederm@xmission.com (Eric W. Biederman)]

Suresh Siddha <suresh.b.siddha@intel.com> writes:

> On Wed, 2009-07-01 at 17:17 -0700, Eric W. Biederman wrote:
>> Suresh Siddha <suresh.b.siddha@intel.com> writes:
>> > Among number of experiments you have tried in the past to fix this, have
>> > you tried the experiment of explicitly clearing the remoteIRR by
>> > changing the trigger mode to edge and then back to level.
>> >
>> > Is there a problem with this?
>> 
>> The problem I had wasn't remoteIRR getting stuck, but the symptoms
>> were largely the same.  I did try changing the trigger mode to edge
>> and back and that did not unstick the ioapic in all cases.
>> 
>
> I did some experiments locally here yesterday and on my old ICH5 based
> system, I couldn't reset the remoteIRR by changing the trigger mode to
> edge and then back to level.
>
> However what worked was an explicit eoi to the io-apic using the
> respective vector.
>
> I guess we need to try both the things based on perhaps io-apic version
> etc.

In part the deep problems I ran into was something other than RemoteIRR.
If it was something as simple as the ioapic being in a documented state
I would have kept looking.  At the very least the RemoteIRR bit was not
set in some of the cases I encountered.

> But what I am nervous about is, did you try both these things aswell and
> still saw stuck interrupts?

Yes.  The work arounds were in the code so I tried them.

> I will cleanup my code and post it, so that we can try on different
> systems. If this still doesn't work on certain HW platforms, atleast our
> experiments of what works and what doesn't work and on what platforms
> will be documented on the web.

Sounds reasonable.  My apologies for the long delayed reply.  I want
to work on this but I have higher priorities.

Eric