> -----Original Message-----
> From: Jan Beulich <[email protected]>
> Sent: 31 July 2020 13:58
> To: Paul Durrant <[email protected]>
> Cc: [email protected]; Paul Durrant <[email protected]>;
> Andrew Cooper
> <[email protected]>; Wei Liu <[email protected]>; Roger Pau Monné
> <[email protected]>
> Subject: Re: [PATCH v2 2/2] x86/hvm: simplify 'mmio_direct' check in
> epte_get_entry_emt()
>
> On 31.07.2020 14:39, Paul Durrant wrote:
> > From: Paul Durrant <[email protected]>
> >
> > Re-factor the code to take advantage of the fact that the APIC access page
> > is
> > a 'special' page.
>
> Hmm, that's going quite as far as I was thinking to go: In
> particular, you leave in place the set_mmio_p2m_entry() use
> in vmx_alloc_vlapic_mapping(). With that replaced, the
> re-ordering in epte_get_entry_emt() that you do shouldn't
> be necessary; you'd simple drop the checking of the
> specific MFN.
Ok, it still needs to go in the p2m though so are you suggesting just calling
p2m_set_entry() directly?
> However, ...
>
> > --- a/xen/arch/x86/hvm/mtrr.c
> > +++ b/xen/arch/x86/hvm/mtrr.c
> > @@ -814,29 +814,22 @@ int epte_get_entry_emt(struct domain *d, unsigned
> > long gfn, mfn_t mfn,
> > return -1;
> > }
> >
> > - if ( direct_mmio )
> > - {
> > - if ( (mfn_x(mfn) ^ mfn_x(d->arch.hvm.vmx.apic_access_mfn)) >>
> > order )
> > - return MTRR_TYPE_UNCACHABLE;
> > - if ( order )
> > - return -1;
>
> ... this part of the logic wants retaining, I think, i.e.
> reporting back to the guest that the mapping needs splitting.
> I'm afraid I have to withdraw my R-b on patch 1 for this
> reason, as the check needs to be added there already.
To be clear... You mean I need the:
if ( order )
return -1;
there?
Paul
>
> Jan
