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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 11/05/2009 10:09, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Depending on what exact plans you have here, I would question whether
> having an upper layer dictate mechanisms used by a lower layer. In
> particular, just like with the same mistake made with kexec,
> - Linux's use of PAT may change (specifically, the value it writes to the PAT
>   MSR may not be statically determinable at some point, making the ELF note
>   approach you indicated as a possible solution unusable)
> - the interface may not be suitable for non-Linux
> Hence I'd appreciate if working out the details here could be done in public.

I was going to suggest put the PAT MSR value in an elfnote, Xen picks up
dom0's note and uses it if possible (Xen relies on PAT[0]=WB,PAT[2]=UC),
else disables PAT for all guest, also advertises PAT feature for any domU PV
guest advertising the exact same PAT MSR value in its elfnote.

Any approach involving Xen dictating to Linux has the fun job of getting
past the kernel maintainers.

 -- Keir



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