linux-kernel - Re: [PATCH v2 4/4] x86/kernel/common.c: Disable SMEP by kernel option nosmep

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Message-ID: <alpine.LFD.2.02.1105162359500.3078@ionos>
Date:	Tue, 17 May 2011 00:01:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Fenghua Yu <fenghua.yu@...el.com>
cc:	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] x86/kernel/common.c: Disable SMEP by kernel option
 nosmep

On Mon, 16 May 2011, Fenghua Yu wrote:
> +/*
> + * If SMEP is supported by the processor, SMEP has been enabled in CR4 earlier.
> + * But if kernel option "nosmep" is given, we disable SMEP here.
> + */
> +static __init void config_smep(struct cpuinfo_x86 *c)
> +{
> +	if (cpu_has(c, X86_FEATURE_SMEP) && unlikely(disable_smep)) {

That unlikely() is completely pointless. This is init code and inside
of a if() already. Where is the point ?

> +		setup_clear_cpu_cap(X86_FEATURE_SMEP);
> +		clear_in_cr4(X86_CR4_SMEP);
> +	}
> +}

Thanks,

	tglx
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