linux-kernel - Re: [PATCH] Fix booting pentium+ with dodgy TSC

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Message-ID: <20080411154310.GA4492@ucw.cz>
Date:	Fri, 11 Apr 2008 17:43:10 +0200
From:	Pavel Machek <pavel@....cz>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, "H. Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	lguest <lguest@...abs.org>
Subject: Re: [PATCH] Fix booting pentium+ with dodgy TSC

On Sun 2008-04-06 17:23:38, Rusty Russell wrote:
> Linus please apply.  Almost by definition this patch can't make things worse.
> 
> We handle a broken tsc these days, so no need to panic.  We clear the TSC bit
> when tsc_init decides it's unreliable (eg. under lguest w/ bad host TSC),
> leading to bogus panic.
> 
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> 
> diff -r 5e0a39f4d07b arch/x86/kernel/cpu/bugs.c
> --- a/arch/x86/kernel/cpu/bugs.c	Sun Apr 06 13:40:39 2008 +1000
> +++ b/arch/x86/kernel/cpu/bugs.c	Sun Apr 06 17:14:12 2008 +1000
> @@ -143,14 +143,6 @@ static void __init check_config(void)
>  #endif
>  
>  /*
> - * If we configured ourselves for a TSC, we'd better have one!
> - */
> -#ifdef CONFIG_X86_TSC
> -	if (!cpu_has_tsc)
> -		panic("Kernel compiled for Pentium+, requires TSC feature!");
> -#endif
> -

CONFIG_X86_TSC means 'cpu has _some_ tsc, rdmsr will work'. If you are
confident noone will read broken tsc, please also remove the config
option. It is meaningless after your patch.
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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