Re: [Xen-devel] [PATCH] xen: grant-table: Simplify get_page_frame

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.09.17 at 18:49, <julien.grall@xxxxxxx> wrote:
> get_page_from_gfn will be able to get reference on foreign page and as
> per my understanding will allow to grant page on foreign memory.
> 
> This was not allowed with a simple get_page(...) on the ARM
> implementation (no sharing nor paging supprot) but is allowed on the x86
> implementation due to get_page_from_gfn.
> 
> On x86, foreign pages are currently only allowed for PVH dom0, so I
> think it is not a big deal for now.
> 
> On Arm, foreign pages can be present on any domain. So this patch would
> permit grant on foreing pages.
> 
> So I would like to check whether it would be valid to grant a mapping on
> foreign pages?

No, I don't think grants should be permitted for other domains'
pages.

> If not, I could add a check if ( p2m_is_foreign(...) ) return
> GTNST_bad_page.

Please do.

> @@ -267,26 +266,20 @@ static int get_paged_frame(unsigned long gfn, unsigned 
> long *frame,
>      if ( !(*page) )
>      {
>          *frame = mfn_x(INVALID_MFN);
> +#if defined(P2M_SHARED_TYPES)

#ifdef please.

>          if ( p2m_is_shared(p2mt) )
>              return GNTST_eagain;
> +#endif
> +#if defined(P2M_PAGES_TYPES)

Same here.

Jan


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