Re: [PATCH v3 06/20] xen/riscv: add root page table allocation

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 8/5/25 12:43 PM, Jan Beulich wrote:

> On 31.07.2025 17:58, Oleksii Kurochko wrote:
> > +static int p2m_alloc_root_table(struct p2m_domain *p2m)
> > +{
> > +    struct domain *d = p2m->domain;
> > +    struct page_info *page;
> > +    const unsigned int nr_root_pages = P2M_ROOT_PAGES;
> > +
> > +    /*
> > +     * Return back nr_root_pages to assure the root table memory is also
> > +     * accounted against the P2M pool of the domain.
> > +     */
> > +    if ( !paging_ret_pages_to_domheap(d, nr_root_pages) )
> > +        return -ENOMEM;
> > +
> > +    page = p2m_allocate_root(d);
> > +    if ( !page )
> > +        return -ENOMEM;
> > +
> > +    p2m->root = page;
> > +
> > +    return 0;
> > +}
> >       
> In the success case, shouldn't you bump the paging pool's total_pages by
> P2M_ROOT_PAGES? (As the freeing side is missing so far, it's not easy to
> tell whether there's [going to be] a balancing problem in the long run.
> In the short run there certainly is.)
>     
I think that total_pages should be updated only in case when page is added
to freelist.
In the case of p2m root table, we just returning some pages to domheap and
durint that decreasing an amount of total_pages as freelist has lesser pages,
and then just allocate pages from domheap without adding them to freelist.

~ Oleksii