Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader

[Borislav Petkov]

On Tue, Apr 28, 2015 at 02:44:28PM -0400, Don Zickus wrote:
> RAS doesn't go through the legacy ports (ie get_nmi_reason()).  Instead it
> triggers the external NMI through a different bit (ioapic I think).

Well, I see it getting registered with __register_nmi_handler() which
adds it to the NMI_LOCAL type, i.e., ghes_notify_nmi() gets called by

default_do_nmi
|-> nmi_handle(NMI_LOCAL, regs, b2b);

AFAICT.

Which explains also the issue we were seeing as that handler is called
on each NMI, even when the machine is running a perf workload.

> The nmi code has no idea what io_remap'ed address apei is using to map its
> error handling register that GHES uses.  Unlike the legacy port which is
> always port 0x61.
> 
> So, with NMI being basically a shared interrupt, with no ability to discern
> who sent the interrupt (and even worse no ability to know how _many_ were sent as
> the NMI is edge triggered instead of level triggered).  As a result we rely
> on the NMI handlers to talk to their address space/registers to determine if
> they were they source of the interrupt.

I was afraid it would be something like that. We probably should poke hw
people to extend that NMI fun so that we can know who caused it.

<snip stuff I agree with>

> Anyway, any ideas or thoughts for improvement are always welcomed. :-)

Yeah, I'm afraid without hw support, that won't be doable. We need the
hw to tell us who caused the NMI. Otherwise we'll be round-robining
(:-)) through handlers like nuts.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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