linux-kernel - Re: ia32_sysenter_target does not preserve EFLAGS

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Date:	Sat, 28 Mar 2015 10:42:27 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: ia32_sysenter_target does not preserve EFLAGS

On Fri, Mar 27, 2015 at 01:09:34PM -0700, Linus Torvalds wrote:
> I think AMD documented that the sti "interrupt shadow" shadows even
> NMI.

Hmm, official docs says this:

"15.21.5 Interrupt Shadows

The x86 architecture defines the notion of an interrupt shadow—a
single-instruction window during which interrupts are not recognized.
For example, the instruction after an STI instruction that sets
EFLAGS.IF (from zero to one) does not recognize interrupts or certain
debug traps."

And I think with "interrupts" this means maskable interrupts, i.e. not
NMI.

STI description itself:

"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."

but there might be some other documentation which I cannot find right
now.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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