linux-kernel - Re: [PATCH] x86 : Ensure X86_FLAGS

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Date:	Mon, 29 Sep 2014 12:17:27 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Anish Bhatt <anish@...lsio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Sebastian Lackner <sebastian@...-team.de>
Subject: Re: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry

On Mon, Sep 29, 2014 at 11:59 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Mon, 29 Sep 2014, Andy Lutomirski wrote:
>> Presumably interrupt delivery clears NT.  I haven't spotted where that's
>> documented yet.
>
> Nope, that's unrelated.

If it weren't the case, then we'd be totally screwed.  Fortunately, it
is.  I found it: SDM Volume 3 6.12.1.2 says:

(On calls to exception and interrupt
handlers, the processor also clears the VM, RF, and NT flags in the
EFLAGS register,
after they are saved on the stack.)

--Andy
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