linux-kernel - Re: [BUG] 2.6.25-rc2-git8 fails to boot on 486 due to TSC breakage

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Date:	Mon, 25 Feb 2008 10:17:33 +0100
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de
Subject: Re: [BUG] 2.6.25-rc2-git8 fails to boot on 486 due to TSC breakage

Ingo Molnar writes:
 > 
 > * H. Peter Anvin <hpa@...or.com> wrote:
 > 
 > > Please fix it in both places.  Using XOR instead of AND-NOT is a bug, 
 > > plain and simple.
 > 
 > yes, i already fixed that when i added Mikael's patch and it's all 
 > queued up.

Ok. For reference and for LKML viewers, this is what
the final patch should be:

diff -rupN linux-2.6.25-rc3/arch/x86/kernel/cpu/common.c linux-2.6.25-rc3.x86-apply-cleared_cpu_caps-correctly/arch/x86/kernel/cpu/common.c
--- linux-2.6.25-rc3/arch/x86/kernel/cpu/common.c	2008-02-25 09:29:03.000000000 +0100
+++ linux-2.6.25-rc3.x86-apply-cleared_cpu_caps-correctly/arch/x86/kernel/cpu/common.c	2008-02-25 09:44:11.000000000 +0100
@@ -504,7 +504,7 @@ void __cpuinit identify_cpu(struct cpuin
 
 	/* Clear all flags overriden by options */
 	for (i = 0; i < NCAPINTS; i++)
-		c->x86_capability[i] ^= cleared_cpu_caps[i];
+		c->x86_capability[i] &= ~cleared_cpu_caps[i];
 
 	/* Init Machine Check Exception if available. */
 	mcheck_init(c);
diff -rupN linux-2.6.25-rc3/arch/x86/kernel/setup_64.c linux-2.6.25-rc3.x86-apply-cleared_cpu_caps-correctly/arch/x86/kernel/setup_64.c
--- linux-2.6.25-rc3/arch/x86/kernel/setup_64.c	2008-02-25 09:29:03.000000000 +0100
+++ linux-2.6.25-rc3.x86-apply-cleared_cpu_caps-correctly/arch/x86/kernel/setup_64.c	2008-02-25 09:44:57.000000000 +0100
@@ -1021,7 +1021,7 @@ void __cpuinit identify_cpu(struct cpuin
 
 	/* Clear all flags overriden by options */
 	for (i = 0; i < NCAPINTS; i++)
-		c->x86_capability[i] ^= cleared_cpu_caps[i];
+		c->x86_capability[i] &= ~cleared_cpu_caps[i];
 
 #ifdef CONFIG_X86_MCE
 	mcheck_init(c);
--
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