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

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Message-ID: <CALCETrWkAnSe6kzha5+MmnZn+YT+rBrmu0vz+9Pr94uUjh9dDQ@mail.gmail.com>
Date:	Wed, 21 May 2014 08:21:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On May 21, 2014 2:46 AM, "Borislav Petkov" <bp@...en8.de> wrote:
>
> 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.

Except that NMI can interrupt #MC at any point as well, I think.

>
> 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?

Exactly.

>
> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --
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