Re: [PATCH v1 1/4] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

[Yu Zhang]

On 8/15/2017 12:40 AM, Paolo Bonzini wrote:
> On 14/08/2017 18:13, Jim Mattson wrote:
> > >                  ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
> > > -               if (efer & EFER_LMA)
> > > -                       rsvd = CR3_L_MODE_RESERVED_BITS & ~CR3_PCID_INVD;
> > > +               if (efer & EFER_LMA) {
> > > +                       u64 maxphyaddr;
> > > +                       u32 eax = 0x80000008;
> > > +
> > > +                       ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL, NULL);
> > > +                       maxphyaddr = eax * 0xff;
> > What if leaf 0x80000008 is not defined?
> I noticed this too, but I thought it was mitigated by being under
> EFER_LMA.  Unfortunately, kvm_set_efer doesn't check
> guest_cpuid_has_longmode, so I guess you do have to test leaf 0x80000000
> first.  Alternatively:
>
> 1) kvm_cpuid could return false if it's falling back to
> check_cpuid_limit, and emulator_get_cpuid can then be changed to return bool
>
> 2) kvm_cpuid and emulator_get_cpuid could gain a new argument to disable
> the check_cpuid_limit fallback.
>
> Yu, would you like to implement the latter?

Thanks for pointing this out, Jim & Paolo. The latter choice sounds 
better to me. :-)
I'd like to implement this in a separate patch in next version patch set.

Yu
> Paolo