linux-kernel - Re: STI architectural question (and lretq -- I'm not even kidding)

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Message-ID: <20140723152311.GC21707@pd.tnic>
Date:	Wed, 23 Jul 2014 17:23:11 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: STI architectural question (and lretq -- I'm not even kidding)

On Wed, Jul 23, 2014 at 08:12:32AM -0700, Andy Lutomirski wrote:
> How are we supposed to survive two machine checks in rapid succession?
> The second will fire as soon as the first one is acked, I imagine.
> Unless we switch stacks before acking the MCE, the return address of
> the first one will be lost.

Oh, that might not fly but in that case the box probably deserves to die
anyway.

I was adressing what you said earlier: "But here's the problem: what
happens if an NMI or MCE happens between the sti and the lretq? I think
an MCE just might be okay -- it's not really recoverable anyway."

An MC Exception can be recoverable and we can recover. The fact that we
raise an exception doesn't always mean we die.

-- 
Regards/Gruss,
    Boris.

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