[Xen-devel] Re: [PATCH 06/16] xen: disable PAT

[Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>]

> Roughly speaking the kernel needs to cope with different values written
> to MSR_IA32_CR_PAT than the single hard coded value it would write
> itself if given the chance. Essentially _PAGE_CACHE_* need to become
> dynamic (or I guess we could change the native layout to match Xen's, I
> don't know why native differs from the initial state, I guess just to
> avoid using the PAT bit for some reason.

Because it is required for some processor variants due to errata. This is
also why the BIOS has them programmed as a mirror between 0-3 and 4-7.

I don't think changing Linux here is the right thing to do - if anything
Xen probably needs to change.

See Xeon errata P21.


Alan

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