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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-12-16 at 15:34 +0000, Julien Grall wrote:
> 
> On 12/16/2013 11:51 AM, 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.
> >
> > 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. :)
> 
> I will remove the comment and modify get_page_from_gfn to handle foreign 
> mapping.

You'll want to coordinate with Mukesh on that latter I think.

Ian.



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