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

[Juergen Gross]

x86 maintainers, could you please consider taking my patch?

There have been several reports now regarding this issue, all could be
fixed using my patch.

Juergen

On 12/17/2014 05:57 AM, Alok Kataria wrote:
> Hi,
>
> On Tue, 2014-12-16 at 10:58 +0100, 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.
>
> Thanks for taking care of this, we are fine with this workaround. On
> newer version of our product, where PAT is virtualized correctly on our
> platform we will go back to using PAT, I will give it a spin sometime
> later to verify it.
>
> Acked-by: Alok N Kataria <akataria@xxxxxxxxxx>
>
> > Reported-by: Jongman Heo <jongman.heo@xxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > Tested-by: Jongman Heo <jongman.heo@xxxxxxxxxxx>
> > ---
> >   arch/x86/mm/pat.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> > index edf299c..7ac6869 100644
> > --- a/arch/x86/mm/pat.c
> > +++ b/arch/x86/mm/pat.c
> > @@ -234,8 +234,13 @@ void pat_init(void)
> >   	      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
> >
> >   	/* Boot CPU check */
> > -	if (!boot_pat_state)
> > +	if (!boot_pat_state) {
> >   		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> > +		if (!boot_pat_state) {
> > +			pat_disable("PAT read returns always zero, disabled.");
> > +			return;
> > +		}
> > +	}
> >
> >   	wrmsrl(MSR_IA32_CR_PAT, pat);
>
> Alok
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