linux-kernel - Re: [RFC] x86_64: A real proposal for iret-less return to kernel

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Date:	Wed, 21 May 2014 11:46:26 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On Tue, May 20, 2014 at 07:39:31PM -0700, Andy Lutomirski wrote:
> So the issue here is that we can have an NMI followed immediately by
> an MCE.

That part might need clarification for me: #MC is higher prio interrupt
than NMI so a machine check exception can interrupt the NMI handler at
any point.

But you're talking only about the small window when nmi_mce_nest_count
hasn't been incremented yet, right? I.e., this:

"The result is that the only interrupt that can happen with
`nmi_mce_nest_count == 0` in NMI context is an MCE at the beginning or
end of the NMI handler."

Correct?

-- 
Regards/Gruss,
    Boris.

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