Re: [PATCH 1/5] x86, mm, pat: Set WT to PA4 slot of PAT MSR

[H. Peter Anvin]

On 09/05/2014 08:22 AM, Toshi Kani wrote:
> On Fri, 2014-09-05 at 08:07 -0700, H. Peter Anvin wrote:
>> On 09/05/2014 07:00 AM, Toshi Kani wrote:
>>>
>>> That's a fine idea, but as Ingo also suggested, I am going to disable
>>> this feature on all Pentium 4 models.  That should give us a safety
>>> margin.  Using slot 4 has a benefit that it keeps the PAT setup
>>> consistent with Xen.      
>>>
>>
>> Slot 4 is also the maximally problematic one, because it is the one that
>> might be incorrectly invoked for the page tables themselves.
> 
> Good point.  I wonder if Xen folks feel strongly about keeping the PAT
> setup consistent with the kernel.  If not, we may choose to use slot 6
> (or 7).
> 

Who cares what the Xen folks "feel strongly about"?  If strong feelings
were a design criterion Xen support would have been pulled from the
kernel a long, long time ago.

The important thing is how to design for the situation that we currently
have to live with.

	-hpa


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