Re: [PATCH v2 for-4.19 3/3] x86/EPT: drop questionable mfn_valid() from epte_get_entry_emt()

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jun 12, 2024 at 05:14:37PM +0200, Jan Beulich wrote:
> On 12.06.2024 17:00, Roger Pau Monné wrote:
> > I wonder if you should explicitly mention that if adding the
> > mfn_valid() check was done to ensure all mappings to MMIO are created
> > with effective UC caching attribute it won't be fully correct either.
> > Xen could map those using a different effective caching attribute by
> > virtue of host MTRRs being in effect plus Xen chosen PAT attributes.
> 
> Well, the mfn_valid() can't have been there to cover _all_ MMIO. It was
> maybe a flawed initial attempt at doing so, and then wasn't properly
> adjusted / dropped. So overall - no, I don't think extending the
> description with anything along the lines of the above would make a lot
> of sense.

I realized myself when writing the paragraph that I wouldn't even know
how to word it properly, neither it would be much helpful without
knowing the exact intention the mfn_valid() check was added for.

Thanks, Roger.