linux-kernel - Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET

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Message-ID: <20080412124947.146865e4@laptopd505.fenrus.org>
Date:	Sat, 12 Apr 2008 12:49:47 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Erik Bosman <ebn310@....vu.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrea Arcangeli <andrea@...share.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC

On Fri, 11 Apr 2008 18:55:58 +0200 (CEST)
Erik Bosman <ebn310@....vu.nl> wrote:

> 
>     x86: Implement prctl PR_GET_TSC and PR_SET_TSC
> 
>     This patch adds a configure option CONFIG_DISABLE_TSC
>     (off by default) for the x86 platform to enable the
>     PR_GET_TSC and PR_SET_TSC commands. These control the
>     ability to use the timestamp counter from userspace
>     (the RDTSC instruction.)
> 
>     This patch uses code earlier used to disable the
>     timestamp counter for the SECCOMP framework. It used
>     to disable the RDTSC on 32 bit kernels, but allow it
>     on x86_64. This patch makes SECCOMP disable the
>     timestamp counter whenever CONFIG_DISABLE_TSC is
>     enabled.


Hi,

why did you make this a configuration option? In general it's not
a good idea to make userspace visible ABI's (PR_* clearly is one of these)
a CONFIG option unless there's some HUGE space saving going on.
I don't see that here....

So can you explain your rationale for making this a config option?

Greetings,
   Arjan van de Ven 

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