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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

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.

> > +int guest_physmap_add_entry(struct domain *d,
> > +                            gfn_t gfn,
> > +                            mfn_t mfn,
> > +                            unsigned long page_order,
> > +                            p2m_type_t t)
> >       
> ... this one, to understand their relationship / difference.
>     
Basically, the difference is only in API and where they are expected to be used:
- guest_physmap_add_entry() to map and set a specific p2m type for a page.
- map_regions_p2mt() to map a region (mostly MMIO) in the guest p2m with
  a specific p2m type.

I added both of them here as they are implemented in a similar way.
I will re-word commit subject and message:
  xen/riscv: implement functions to map memory in guest p2m

  Introduce guest_physmap_add_entry() to map a page and assign a specific
  p2m type, and map_regions_p2mt() to map a region (typically MMIO) in
  the guest p2m with a designated p2m type.

  Currently, this functionality is not fully operational, as p2m_set_entry()
  still returns -EOPNOTSUPP.

  Additionally, introduce p2m_write_(un)lock() to protect modifications to
  the p2m page tables, along with p2m TLB flush helpers to ensure proper
  TLB invalidation (if necessary) when the p2m lock is released.

~ Oleksii