[Xen-devel] Re: c/s 19576 vs. AMD systems

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 29.04.09 11:43 >>>
>On 29/04/2009 09:53, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> I'm afraid this change is going to hurt on AMD systems where memory extends
>> beyond the 4Gb boundary: Both such systems that I have direct access to
>> have their Intel MTRRs only defined up to the 4Gb boundary, yet through
>> the use of AMD specific MSRs (SYS_CFG.Tom2ForceMemTypeWB and TOM2)
>> the default memory type for everything beyond the 4Gb boundary is WB.
>> On these systems there shouldn't be any clipping. I certainly can put 
>> together
>> a patch for this, but it'll take me a couple of days until I'd get to it.
>
>What do you suggest? Make the clip Intel-specific? We've only seen problems
>with (a very few) Intel boxes, so handling AMD at all may be quite
>unnecessary.

No - if BIOSes are broken, they can as well be an AMD systems. I'd rather
take TOM2 and the mentioned SYS_CFG bit into account in that code (not
the least because modern Linux also does so in its MTRR handling code).

Jan


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