RE: [PATCH v2 2/2] x86/hvm: simplify 'mmio_direct' check in epte_get_entry_emt()

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 31 July 2020 14:41
> To: paul@xxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; 'Paul Durrant' <pdurrant@xxxxxxxxxx>; 
> 'Andrew Cooper'
> <andrew.cooper3@xxxxxxxxxx>; 'Wei Liu' <wl@xxxxxxx>; 'Roger Pau Monné' 
> <roger.pau@xxxxxxxxxx>
> Subject: Re: [PATCH v2 2/2] x86/hvm: simplify 'mmio_direct' check in 
> epte_get_entry_emt()
> 
> On 31.07.2020 15:07, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: 31 July 2020 13:58
> >> To: Paul Durrant <paul@xxxxxxx>
> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Paul Durrant <pdurrant@xxxxxxxxxx>; 
> >> Andrew Cooper
> >> <andrew.cooper3@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger Pau Monné 
> >> <roger.pau@xxxxxxxxxx>
> >> 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 <pdurrant@xxxxxxxxxx>
> >>>
> >>> 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?
> 
> Yes, if this works. The main question really is whether there are
> any hidden assumptions elsewhere that this page gets mapped as an
> MMIO one.
>

Actually, it occurs to me that logdirty is going to be an issue if I use 
p2m_ram_rw. If I'm not going to use p2m_mmio_direct then do you have another 
suggestion?

  Paul