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[PATCH] Fix booting pentium+ with dodgy TSC

Previous thread: [patch] checkpatch: relax spacing and line length by Jan Engelhardt on Sunday, April 6, 2008 - 12:54 am. (33 messages)

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[view original message]
From: Rusty Russell <rusty@...>
To: Linus Torvalds <torvalds@...>
Cc: Andi Kleen <ak@...>, H. Anvin <hpa@...>, <linux-kernel@...>, Ingo Molnar <mingo@...>, lguest <lguest@...>
Subject: [PATCH] Fix booting pentium+ with dodgy TSC
Date: Sunday, April 6, 2008 - 3:23 am

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@rustcorp.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

-

-/*

  * If we were told we had a good local APIC, check for buggy Pentia,

  * i.e. all B steppings and the C2 stepping of P54C when using their

  * integrated APIC (see 11AP erratum in "Pentium Processor

--
[view original message]
From: Pavel Machek <pavel@...>
To: Rusty Russell <rusty@...>
Cc: Linus Torvalds <torvalds@...>, Andi Kleen <ak@...>, H. Anvin <hpa@...>, <linux-kernel@...>, Ingo Molnar <mingo@...>, lguest <lguest@...>
Subject: Re: [PATCH] Fix booting pentium+ with dodgy TSC
Date: Friday, April 11, 2008 - 11:43 am

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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[view original message]
From: Ingo Molnar <mingo@...>
To: Rusty Russell <rusty@...>
Cc: Linus Torvalds <torvalds@...>, Andi Kleen <ak@...>, H. Anvin <hpa@...>, <linux-kernel@...>, lguest <lguest@...>, Thomas Gleixner <tglx@...>
Subject: Re: [PATCH] Fix booting pentium+ with dodgy TSC
Date: Sunday, April 6, 2008 - 7:22 am

well, while i agree with the patch it could make things worse. In this

case it can cause code that has been compiled to rely on TSC to

malfunction. For if sched_clock() was using cpu_has_tsc it could return

0 all the time, breaking the scheduler without the user having a clear

idea why it broke. It isnt, and sched_clock() will work fine, but still,

your "this cant make things worse" statement is not completely correct. 


In any case:


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


and i've also queued it up into the for-.25 queue of x86.git.


	Ingo

--
[view original message]
From: Rusty Russell <rusty@...>
To: Ingo Molnar <mingo@...>
Cc: Linus Torvalds <torvalds@...>, Andi Kleen <ak@...>, H. Anvin <hpa@...>, <linux-kernel@...>, lguest <lguest@...>, Thomas Gleixner <tglx@...>
Subject: Re: [PATCH] Fix booting pentium+ with dodgy TSC
Date: Sunday, April 6, 2008 - 4:29 pm

Hence the "almost".  It can't break machines, but it could make the problem

harder to diagnose.  Given that it will unbreak at least one machine, I'm 


Thanks!

Rusty.

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Previous thread: [patch] checkpatch: relax spacing and line length by Jan Engelhardt on Sunday, April 6, 2008 - 12:54 am. (33 messages)

Next thread: Re: + acpi-fix-bug-10124.patch added to -mm tree by Yinghai Lu on Sunday, April 6, 2008 - 3:26 am. (4 messages)