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

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Message-ID: <20140723094038.GA23102@pd.tnic>
Date:	Wed, 23 Jul 2014 11:40:38 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"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 Tue, Jul 22, 2014 at 06:03:35PM -0700, Linus Torvalds wrote:
> So I'm afraid that "sti; lret" is not guaranteed to be architecturally
> NMI-safe. But it *might* be safe on certain micro-architectures, and
> maybe somebody inside Intel or AMD can give us a hint about when it is
> safe and when it isn't.

>From AMD's APM, STI section:

"Sets the interrupt flag (IF) in the rFLAGS register to 1, thereby
allowing external interrupts received on the INTR input. Interrupts
received on the non-maskable interrupt (NMI) input are not affected by
this instruction."

-- 
Regards/Gruss,
    Boris.

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