Re: [PATCH] x86: don't rely on VMWare emulating PAT MSR correctly

[Juergen Gross]

On 12/16/2014 05:47 PM, H. Peter Anvin wrote:
> On 12/16/2014 01:58 AM, Juergen Gross wrote:
> > VMWare seems not to emulate the PAT MSR correctly: reaeding
> > MSR_IA32_CR_PAT returns 0 even after writing another value to it.
> >
> > Detect this bug and don't use the read value if it is 0.
> >
> > Commit bd809af16e3ab1f8d55b3e2928c47c67e2a865d2 ("x86: Enable PAT to
> > use cache mode translation tables") triggers this VMWare bug when the
> > kernel is booted as a VMWare guest.
> >
> > Reported-by: Jongman Heo <jongman.heo@xxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > Tested-by: Jongman Heo <jongman.heo@xxxxxxxxxxx>
>
> I presume cachability control is irrelevant for a VMware guest?  I'm
> wondering if it would be better to just plain ignore the failure rather
> than disabling PAT.

I'd rather disable PAT as this seems to be like a PAT erratum.

In case you want to keep PAT active I can redo the patch to not rely on
the read MSR value in the non-Xen case (under Xen reading the MSR is the
only way to obtain the correct settings).

Juergen

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