linux-kernel - Re: 64bit x86: NMI nesting still buggy?

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Date:	Thu, 1 May 2014 00:10:58 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Salman Qazi <sqazi@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Michal Hocko <mhocko@...e.cz>, Borislav Petkov <bp@...en8.de>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Petr Tesarik <ptesarik@...e.cz>, Petr Mladek <pmladek@...e.cz>
Subject: Re: 64bit x86: NMI nesting still buggy?

On Tue, 29 Apr 2014, H. Peter Anvin wrote:

> > [2] 	"A special case can occur if an SMI handler nests inside an NMI 
> > 	 handler and then another NMI occurs. During NMI interrupt 
> > 	 handling, NMI interrupts are disabled, so normally NMI interrupts 
> >  	 are serviced and completed with an IRET instruction one at a 
> > 	 time. When the processor enters SMM while executing an NMI 
> > 	 handler, the processor saves the SMRAM state save map but does 
> > 	 not save the attribute to keep NMI interrupts disabled. 
> > 	 Potentially, an NMI could be latched (while in SMM or upon exit) 
> > 	 and serviced upon exit of SMM even though the previous NMI  
> > 	 handler has still not completed."
> 
> I believe [2] only applies if there is an IRET executing inside the SMM
> handler, which should not normally be the case.  It might also have been
> addressed since that was written, but I don't know.

Is there any chance that Intel would reveal what's behind this paragraph 
and how likely it is to expect such BIOSes in the wild?

Thanks,

-- 
Jiri Kosina
SUSE Labs
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