Re: [Xen-devel] [RFC 09/16] xen/arm: p2m: Introduce a function to resolve translation fault

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 4 Dec 2018, Julien Grall wrote:
> Hi Stefano,
> 
> On 11/12/18 11:36 PM, Stefano Stabellini wrote:
> > On Mon, 12 Nov 2018, Julien Grall wrote:
> > > Hi Stefano,
> > > 
> > > On 11/6/18 2:20 PM, Julien Grall wrote:
> > > > On 05/11/2018 17:56, Stefano Stabellini wrote:
> > > > > On Mon, 5 Nov 2018, Julien Grall wrote:
> > > > > > On 02/11/2018 23:27, Stefano Stabellini wrote:
> > > > > > > On Mon, 8 Oct 2018, Julien Grall wrote:
> > > > > > > 
> > > > > > > > +    /*
> > > > > > > > +     * Now that the work on the entry is done, set the valid
> > > > > > > > bit to
> > > > > > > > prevent
> > > > > > > > +     * another fault on that entry.
> > > > > > > > +     */
> > > > > > > > +    resolved = true;
> > > > > > > > +    entry.p2m.valid = 1;
> > > > > > > > +
> > > > > > > > +    p2m_write_pte(table + offsets[level], entry,
> > > > > > > > p2m->clean_pte);
> > > > > > > > +
> > > > > > > > +    /*
> > > > > > > > +     * No need to flush the TLBs as the modified entry had the
> > > > > > > > valid bit
> > > > > > > > +     * unset.
> > > > > > > > +     */
> > > > > > > > +
> > > > > > > > +out_unmap:
> > > > > > > > +    unmap_domain_page(table);
> > > > > > > > +
> > > > > > > > +out:
> > > > > > > > +    p2m_write_unlock(p2m);
> > > > > > > > +
> > > > > > > > +    return resolved;
> > > > > > > > +}
> > > > > > > > +
> > > > > > > >     static inline int p2m_insert_mapping(struct domain *d,
> > > > > > > >                                          gfn_t start_gfn,
> > > > > > > >                                          unsigned long nr,
> > > > > 
> > > > > 
> > > > > We probably want to update the comment on top of the call to
> > > > > p2m_resolve_translation_fault:
> > > > 
> > > > Whoops. I will fix it.
> > > 
> > > Looking at this again. I think the comment on top of the call to
> > > p2m_resolve_translation_fault still makes sense. Feel free to suggest an
> > > update of the comment if you think it is not enough.
> > 
> >          /*
> >           * The PT walk may have failed because someone was playing with
> >           * the Stage-2 page table or because the valid bit was left
> >           * unset to track memory accesses. In these cases, we want to
> >           * return to the guest.
> >           */
> 
> Thank you for the suggestion. Thinking a bit more,  I would not be surprised
> we decide to expand p2m_resolve_translation_fault in the future. So I decided
> to go for a more generic comment to avoid stale comment:
> 
>        /*
>       * First check if the translation fault can be resolved by the
>       * P2M subsystem. If that's the case nothing else to do.

OK

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