linux-kernel - Re: [PATCH] i386: Prevent early access to TSC to avoid crash on TSCless systems

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Date:	Sat, 24 Mar 2007 23:09:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Adrian Bunk <bunk@...sta.de>
Subject: Re: [PATCH] i386: Prevent early access to TSC to avoid crash on TSCless systems


* Thomas Gleixner <tglx@...utronix.de> wrote:

> commit f9690982b8c2f9a2c65acdc113e758ec356676a3 removed the check for 
> cpu_khz from sched_clock(), which prevented early access to the TSC by 
> non obvious magic.
> 
> This is harmless as long as the CPU has a TSC. On TSCless systems this 
> results in an illegal instruction trap.
> 
> Replace tsc_disabled and tsc_unstable by tsc_enabled, which is only 
> set when the tsc is available and not unstable.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

oops, indeed! I think this should also resolve one of the bugs (TSC-less 
Cyrix?) that were reported against -mm some time ago.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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