Re: 64bit x86: NMI nesting still buggy?

[Borislav Petkov]

On Wed, May 21, 2014 at 03:42:24PM +0200, Jiri Kosina wrote:
> Alright, Andy's iret optimization efforts do immediately bring a
> followup question -- why is this not a problem with iret-based return
> from #MC possibly interrupting NMI?

Yeah, and frankly, I don't see this nesting fun at all protected against
a #MC interrupting it at any point actually. Because once the #MC
handler returns, it goes into paranoid_exit and that place doesn't
account for NMIs at all, AFAICS.

Which would mean:

* NMI goes off
* MCE happens, we switch to machine_check which is paranoidzeroentry
* #MC handler is done -> paranoid_exit -> IRET
-> boom! Or if not "boom", at least, the NMI gets forgotten.

Am I missing something?

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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