Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR

[Xiao Guangrong]

On 07/13/2015 11:13 PM, Paolo Bonzini wrote:
> On 13/07/2015 16:45, Xiao Guangrong wrote:
> > > +    /* MTRR is completely disabled, use UC for all of physical
> > > memory. */
> > > +    if (!(mtrr_state->enabled & 0x2))
> > > +        return MTRR_TYPE_UNCACHABLE;
> > >
> > > actually disappears in commit fa61213746a7 (KVM: MTRR: simplify
> > > kvm_mtrr_get_guest_memory_type, 2015-06-15).
> >
> > :(
> >
> > Based on the SDM, UC is applied to all memory rather than default-type
> > if MTRR is disabled.
>
> There are two issues I think.  One is that I cannot find in the current
> code that "UC is applied to all memory rather than default-type if MTRR
> is disabled".  mtrr_default_type unconditionally looks at
> mtrr_state->deftype.

Yes... Will fix.

> > However, fast boot came back if "return 0xFF" here. So fast boot expects
> > that the memory type is WB.
>
> Yes.
>
> > > static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
> > > {
> > >           if (mtrr_is_enabled(mtrr_state))
> > >                   return mtrr_state->deftype &
> > > IA32_MTRR_DEF_TYPE_TYPE_MASK;
> > >           else
> > >                   return MTRR_TYPE_UNCACHABLE;
> > > }
> > >
> > > ?  Then it's easy to add a quirk that makes the default WRITEBACK until
> > > MTRRs are enabled.
> >
> > It is the wrong configure in OVMF... shall we need to adjust KVM to satisfy
> > OVMF?
>
> That's what quirks are for...  The firmware should still be fixed of course.

I see, will do it.
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