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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.

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.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel