Re: [PATCH v3 14/19] xen/arm: add Persistent Map (PMAP) infrastructure

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 28/02/2022 10:30, Jan Beulich wrote:
> On 28.02.2022 11:20, Julien Grall wrote:
> > On 28/02/2022 10:10, Jan Beulich wrote:
> > > On 28.02.2022 10:55, Julien Grall wrote:
> > > > On 22/02/2022 15:22, Jan Beulich wrote:
> > > > > On 21.02.2022 11:22, Julien Grall wrote:
> > > > > > +    /*
> > > > > > +     * We cannot use set_fixmap() here. We use PMAP when there is no direct 
> > > > > > map,
> > > > > > +     * so map_pages_to_xen() called by set_fixmap() needs to map pages on
> > > > > > +     * demand, which then calls pmap() again, resulting in a loop. Modify the
> > > > > > +     * PTEs directly instead. The same is true for pmap_unmap().
> > > > > > +     */
> > > > > > +    arch_pmap_map(slot, mfn);
> > > > > I'm less certain here, but like above I'm under the impression
> > > > > that this comment may no longer be accurate.
> > > > This comment is still accurate for Arm. I also expect it to be accurate
> > > > for all architectures because set_fixmap() is likely going to be
> > > > implemented with generic PT helpers.
> > > >
> > > > So I think it makes sense to keep it in common code. This explains why
> > > > we are calling arch_pmap_map() rather than set_fixmap() directly.
> > > I guess I was rather after "when there is no direct map" alluding to the
> > > planned removal of it on x86.
> > It is one way to interpret it. The other way is that pmap will be used
> > when the directmap is not yet in place.
> >
> > But I guess I could be less specific and refers to the fact the domain
> > page infrastructure is not yet setup. Would that be better for you?
> That or simply add "(yet)" to what is there.
I will do that in the next version.

Thanks!

Cheers,

--
Julien Grall