linux-kernel - Re: [PATCH v2 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace

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Message-ID: <542B8C7F.70108@fds-team.de>
Date:	Wed, 01 Oct 2014 07:09:19 +0200
From:	Sebastian Lackner <sebastian@...-team.de>
To:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
CC:	Anish Bhatt <anish@...lsio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace

> +	testl $X86_EFLAGS_NT,EFLAGS(%rsp)	/* saved EFLAGS match cpu */
> +	jz 1f
> +	pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
> +	popfq_cfi
> +1:
> +

Do you think it makes sense to change the order here, so that no jump happens if
NT is not set (which happens a bit more often, than the other way round)? Just a
guess though, haven't measured if pipeline effects have such a big influence in this
case. ;)

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