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SubjectRe: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"
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On Thu, 2016-03-10 at 14:04 -0500, Paul Gortmaker wrote:
> [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> disabled"] On 10/03/2016 (Thu 18:20) Borislav Petkov wrote:
>
> > On Thu, Mar 10, 2016 at 09:49:51AM -0700, Toshi Kani wrote:
> > > This confirms the issue - QEMU's virtual Intel CPU does not support
> > > MTRR. 
> > >
> > > When MTRR is disabled, the kernel does not call pat_init().
> > >  pat_enabled() is still set to true when CONFIG_X86_PAT is set.
> > >  CONFIG_X86_PAT depends on CONFIG_MTRR, and assumes that MTRR is
> > > enabled. 
> >
> > Aha, so "qemu32" model doesn't support MTRRs but "kvm32" does, for
> > example. And so do the majority of the other CPU types.
>
> So, I guess that is a qemu bug?  If there is no real silicon out there
> that has no MTRR but does claim PAT, then qemu32 is a flawed CPU type?

It turns out that your qemu's virtual CPU does not support PAT, either. :-)
 So, it is consistent on this regard.  I will send patches to address this
issue.

Thanks,
-Toshi

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