Re: [Xen-devel] Xen 4.5 random freeze question

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Already posted:

http://marc.info/?l=xen-devel&m=141648092100568

Ian hasn't provided any feedback yet.

On Thu, 20 Nov 2014, Andrii Tseglytskyi wrote:
> I think I'll debug this a bit later - unfortunately, now don't have
> time for this. But I want to get rid of spurious interrupt here.
> 
> BTW - Stefano are you going to post the patch that we created
> yesterday ? Will Ian accept it?
> 
> Regards,
> Andrii
> 
> On Thu, Nov 20, 2014 at 1:15 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > On 11/20/2014 10:28 AM, Stefano Stabellini wrote:
> >> On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >>> 19 ÐÐÑÑ. 2014 20:32, ÐÐÑÐÑÑÑÐÐÑ "Stefano Stabellini" 
> >>> <stefano.stabellini@xxxxxxxxxxxxx> ÐÐÐÐÑÐÐ:
> >>>>
> >>>> On Wed, 19 Nov 2014, Julien Grall wrote:
> >>>>> On 11/19/2014 06:14 PM, Stefano Stabellini wrote:
> >>>>>> That's right, the maintenance interrupt handler is not called, but it
> >>>>>> doesn't do anything so we are fine. The important thing is that an
> >>>>>> interrupt is sent and git_clear_lrs gets called on hypervisor entry.
> >>>>>
> >>>>> It would be worth to write down this somewhere. Just in case someone
> >>>>> decide to add code in maintenance interrupt later.
> >>>>
> >>>> Yes, I could add a comment in the handler
> >>>
> >>> Maybe it wouldn't take a lot of effort to fix it? I am just worrying that 
> >>> we may hide some issue -
> >>> typically spurious interrupt this not what is expected.
> >>
> >> My guess is that by clearing UIE before reading GICC_IAR, we "clear" the
> >> maintenance interrupt too, as a consequence the following read to
> >> GICC_IAR would return 1023 (nothing to be read). As bit as if the
> >> maintenance interrupt was a level interrupt and we just disabled it.
> >>
> >> So I think that if we cleared UIE after reading GICC_IAR, GICC_IAR would
> >> return the correct value.
> >>
> >> However with the current structure of the code, the first thing that we
> >> do upon entering the hypervisor is clearing LRs and given what happened
> >> on your platform I think is a good idea to do it with UIE disabled.
> >
> > Agreed. UIE should be disabled to avoid another maintenance interrupt as
> > soon as we EOI the IRQ.
> >
> >> This is way I would rather read spurious interrupts but read/write LRs
> >> with UIE disabled than reading maintenance interrupts but risking
> >> strange behaviours on some platforms.
> >
> > Reading the GIC-v2 documentation, the spurious interrupt things should
> > happen on any platform every time the UIE is disabled while we receive a
> > maintenance interrupt.
> >
> > "The read returns a spurious interrupt ID of 1023 if any of the
> > following apply:
> >
> > - no pending interrupt on the CPU interface has sufficient priority for
> > the interface to signal it to the processor"
> >
> > --
> > Julien Grall
> 
> 
> 
> -- 
> 
> Andrii Tseglytskyi | Embedded Dev
> GlobalLogic
> www.globallogic.com
>

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