Re: [Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Wednesday 17 September 2008 11:20:57 Jiang, Yunhong wrote:
> >-----Original Message-----
> >From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> >[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jan Beulich
> >Sent: 2008å9æ17æ 15:06
> >To: Christoph Egger; Gavin Maltby
> >Cc: Haitao Shan; Tian, Kevin; xen-devel@xxxxxxxxxxxxxxxxxxx;
> >Shan, Haitao; Keir Fraser
> >Subject: Re: [Xen-devel] Re: [PATCH 1/4] CPU online/offline
> >support in Xen
> >
> >>>> Gavin Maltby <Gavin.Maltby@xxxxxxx> 17.09.08 06:17 >>>
> >>
> >>I don't see this as a problem for machine check correctness.
> >>
> >>If dom0 asks to offline a cpu (because it believes the cpu is
> >
> >busted and
> >
> >>a threat to uptime), that decision is fundamentally asynchronous
> >>to the actual error handling that occured at machine check exception
> >>time:
> >>
> >>  - running in whatever context
> >>  - MCE occurs
> >>  - trap to hypervisor MCE handler
> >>       . this decides on hypervisor panic, or other appropriate
> >>         immediate (in handler) response
> >>       . telemetry forwarded to dom0 for logging and analysis
> >>  - assume no hypervisor panic
> >>  - eons pass during which any unconstrained bad data remaining
> >>    after initial handling may go anywhere
> >>  - dom0 gets telemetry and let's say diagnoses a fault and
> >>    decides to call back into the hypervisor to offline the
> >>    offending cpu
> >>
> >>Note the "eons pass" bit;  tonnes of instructions may run on the
> >>bad cpu in this time, and a few more for some offline delay won't
> >>hurt.
> >
> >Shouldn't this possibly be handled the other way around: If a
> >recoverable
> >MCE happened, immediately stop scheduling anything on the affected
> >CPU(s), until Dom0 tells you otherwise (and of course as long as there
> >remains at least one CPU to run on).
>
> Current MCE handling in Xen has no mechanism to achieve this.

It has since c/s 17968.

Christoph



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