Re: [PATCH v2 10/17] xen/riscv: implement guest_physmap_add_entry() for mapping GFNs to MFNs

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 7/3/25 3:09 PM, Jan Beulich wrote:

> On 03.07.2025 13:54, Oleksii Kurochko wrote:
> > On 7/3/25 1:33 PM, Jan Beulich wrote:
> > > On 03.07.2025 13:02, Oleksii Kurochko wrote:
> > > > On 6/30/25 5:59 PM, Jan Beulich wrote:
> > > > > On 10.06.2025 15:05, Oleksii Kurochko wrote:
> > > > > > +                              unsigned long nr, mfn_t mfn, p2m_type_t t)
> > > > > > +{
> > > > > > +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
> > > > > > +    int rc;
> > > > > > +
> > > > > > +    p2m_write_lock(p2m);
> > > > > > +    rc = p2m_set_entry(p2m, start_gfn, nr, mfn, t, p2m->default_access);
> > > > > > +    p2m_write_unlock(p2m);
> > > > > > +
> > > > > > +    return rc;
> > > > > > +}
> > > > > > +
> > > > > > +int map_regions_p2mt(struct domain *d,
> > > > > > +                     gfn_t gfn,
> > > > > > +                     unsigned long nr,
> > > > > > +                     mfn_t mfn,
> > > > > > +                     p2m_type_t p2mt)
> > > > > > +{
> > > > > > +    return p2m_insert_mapping(d, gfn, nr, mfn, p2mt);
> > > > > > +}
> > > > > >               
> > > > > What is this function doing here? The description says "for generic mapping
> > > > > purposes", which really may mean anything. Plus, if and when you need it, it
> > > > > wants to come with a name that fits with e.g. ...
> > > > >             
> > > > These names are used across the common code and various architectures. Not all
> > > > architectures need to implement all of these functions.
> > > > I believe|guest_physmap_add_page()| (which internally calls|guest_physmap_add_entry()|)
> > > > is needed to be implemented for all architectures, while|map_regions_p2mt()| is used
> > > > by Arm and the common Dom0less-related code, and because of RISC-V is going to re-use
> > > > common Dom0less code it is implementing this function too.
> > > >           
> > > First, my comment was solely about this one function above. And then I didn't
> > > even know Arm had such a function. It's not used from common code (except again
> > > from dom0less code where it should have been better abstracted, imo). I'm also
> > > not surprised I wasn't aware of it since, as can be implied from the above,
> > > otherwise I would likely have complained about its name not fitting the general
> > > scheme (which isn't all that good either).
> > >         
> > If I'm right, there is nothing similar to|map_regions_p2mt()| in the common headers.
> >
> > Anyway, I think we could follow up with a patch to rename this function to
> > something more appropriate.
> >
> > I was thinking about adding something like|map_regions_to_guest()|,|map_p2m_regions()|,
> > or|map_p2m_memory()| to|xen/mm.h|, along with proper renaming in the Arm code.
> >
> > Does that make sense?
> >       
> Imo that seemingly redundant function (i.e. if it's really needed) would want
> to be named guest_physmap_<whatever>().
>     
If it is redundant what is expected to be used instead to map_regions_p2mt() to map MMIO,
for example, to guest: guest_physmap_add_page()? Based on the comment above the definition
of this function it is for RAM: /* Untyped version for RAM only, for compatibility */

~ Oleksii