Re: [Xen-devel] [PATCH v4 08/11] xen/arm: Handle remove foreign mapping

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-12-16 at 12:51 +0100, Tim Deegan wrote:
> At 19:37 +0000 on 13 Dec (1386959858), Julien Grall wrote:
> > @@ -693,12 +694,21 @@ long do_memory_op(unsigned long cmd, 
> > XEN_GUEST_HANDLE_PARAM(void) arg)
> >              return rc;
> >          }
> >  
> > -        page = get_page_from_gfn(d, xrfp.gpfn, NULL, P2M_ALLOC);
> > +        /*
> > +         * If autotranslate guest, (eg pvh), the gfn could be mapped to a 
> > mfn
> > +         * from foreign domain by the user space tool during domain 
> > creation.
> > +         * We need to check for that, free it up from the p2m, and release
> > +         * refcnt on it. In such a case, page would be NULL and the 
> > following
> > +         * call would not have refcnt'd the page.
> > +         */
> > +        page = get_page_from_gfn(d, xrfp.gpfn, &p2mt, P2M_ALLOC);
> >          if ( page )
> >          {
> >              guest_physmap_remove_page(d, xrfp.gpfn, page_to_mfn(page), 0);
> >              put_page(page);
> >          }
> > +        else if ( p2m_is_foreign(p2mt) )
> > +            rc = p2m_remove_foreign(d, xrfp.gpfn);
> 
> This doesn't seem like the right interface -- having special cases
> like this in the callers is something we slipped into in x86 for a lot
> of the paging/sharing code and it's not nice.  I think maybe we can
> just have get_page_from_gfn() DTRT for foreign (and grant) entries.

DYM guest_physmap_remove_page?

I asked Mukesh a few times to make get_page_from_gfn handle the foreign
page refcounting and return a valid struct page_info *.

> Also, the comment will have been out of data by the time the x86
> version of this code is finished, as we won't be handling the refcount
> at this level. :)




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