linux-kernel - Re: patch disabling use of PSE on Atom CPUs with a certain erratum

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Message-Id: <4CAE0373020000780001B50E@vpn.id2.novell.com>
Date:	Thu, 07 Oct 2010 16:29:23 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: patch disabling use of PSE on Atom CPUs with a certain
	 erratum

>>> On 07.10.10 at 17:10, "H. Peter Anvin" <hpa@...or.com> wrote:
> On 10/07/2010 07:52 AM, Jan Beulich wrote:
>>>>> On 07.10.10 at 16:08, "H. Peter Anvin" <hpa@...or.com> wrote:
>>> On 10/07/2010 07:01 AM, Jan Beulich wrote:
>>>>>
>>>>> Those Atoms don't have 64-bit support.
>>>>
>>>> That's different from what I found looking around on the web.
>>>>
>>>
>>> Do tell...
>> 
>> E.g.
>> 
>> http://en.wikipedia.org/wiki/List_of_Intel_Atom_microprocessors 
>> 
>> in particular the Atom 230 and Atom 330 (which to my reading match
>> the spec updates for the 200 and 300 series, which in turn exhibit
>> the erratum in question).
>> 
> 
> You're right... I misremembered.  The question is what to do at this
> point, since we're already in trouble.  A possible failure on startup
> seems better than a state in which we could get data corruption at
> almost any time.

The only possible (afaict) way to address this would be to check for
the erratum in the boot code, and establish 4k page mappings from
the beginning. That's likely going to be ugly though.

The main reason I was asking was not so much to trigger a code
change, but to understand the implications (since both the comment
in the code and the changeset comment don't really hint at this
leaving a problem open for 64-bit), to some degree to understand
whether e.g. Xen would also need such a workaround (if anyone
cares to run Xen on Atoms).

Jan

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