linux-kernel - Re: [PATCH] x86: Disable 4MB page tables for Atom, work around errata AAE44

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Message-ID: <4BC33022.3000608@zytor.com>
Date:	Mon, 12 Apr 2010 07:37:22 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Colin King <colin.king@...onical.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Disable 4MB page tables for Atom, work around errata
 AAE44

On 04/12/2010 01:02 AM, Andi Kleen wrote:
> Colin King <colin.king@...onical.com> writes:
>>  
>> +static void __init check_atom(void)
>> +{
>> +
>> +	/*
>> +	 *  Disable 4MB page tables to work around Intel errata AAE44 for
>> +	 *  Atom. We cannot guarantee stopping undefined processor behaviour
>> +	 *  when two pageing structure translations differ with respect to
>> +	 *  page frame sizes.  Hence, for Atoms we disable the PSE.
>> +	 */
>> +	if (boot_cpu_data.x86_model == 0x1c) {
> 
> Perhaps someone else pointed that out already, but you obviously
> need to check for x86_vendor == X86_VENDOR_INTEL and x86_family == 6 too,
> otherwise you'll get false positives.
> 
> Besides such workarounds are normally in arch/x86/kernel/cpu/intel.c.
> bugs.c is really obsolete.
> 

Much more than that, the constraint is clearly not strict enough.  I'm
currently trying to work out internally what the actual constraint
should be (it's a bit of a documentation hole at the moment.)

	-hpa

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