Re: [Xen-devel] [PATCH MM-PART3 v3 6/9] xen/arm: mm: Use {, un}map_domain_page() to map/unmap Xen page-tables

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 6/14/19 10:00 PM, Stefano Stabellini wrote:
> On Fri, 14 Jun 2019, Julien Grall wrote:
> > Currently, the virtual address of the 3rd level page-tables is obtained
> > using mfn_to_virt().
> >
> > On Arm32, mfn_to_virt can only work on xenheap page. While in theory
> > all the page-tables updated will reside in xenheap, in practice the
> > page-tables covering Xen memory (e.g xen_mapping) is part of Xen binary.
> >
> > Furthermore, a follow-up change will update xen_pt_update_entry() to
> > walk all the levels and therefore be more generic. Some of the
> > page-tables will also part of Xen memory and therefore will not be
> > reachable using mfn_to_virt().
> >
> > The easiest way to reach those pages is to use {, un}map_domain_page().
> > While on arm32 this means an extra mapping in the normal cases, this is not
> > very important as xen page-tables are not updated often.
> >
> > In order to allow future change in the way Xen page-tables are mapped,
> > two new helpers are introduced to map/unmap the page-tables.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> > Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
> >
> > ---
> >      Changes in v3:
> >          - Fix typo in the commit message
> >          - Add Stefano's acked-by
> It didn't stick, so:
>
> Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> :-)
Whoops yes. Thankfully I didn't add an ack by mistake this time :).

Cheers,

--
Julien Grall

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