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

[Tim Deegan <tim@xxxxxxx>]

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. :)

Tim.


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