Re: [Xen-devel] [PATCH MM-PART3 v2 09/12] xen/arm: mm: Use {, un}map_domain_page() to map/unmap Xen page-tables

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 13 Jun 2019, Julien Grall wrote:
> Hi Stefano,
> 
> On 6/12/19 11:25 PM, Stefano Stabellini wrote:
> > On Tue, 14 May 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 practice
> > > all the page-tables updated will reside in xenheap, in practive the
> >                                                          ^ in theory ?
> 
> The first one should to be "theory" and the second "practice". Because some of
> the bootstrap page-tables (e.g xen_fixmap/xen_mapping) are part of Xen binary.
> 
> > 
> > 
> > > 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>
> > 
> > aside from the typo above:
> 
> Let me know if my suggestion makes sense above.

Yes, fine


> > Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> 
> Thank you.
> 
> Cheers,
> 
> -- 
> Julien Grall
> 

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