Re: [PATCH V6 2/2] libxl/arm: Add handling of extended regions for DomU

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Stefano Stabellini writes ("Re: [PATCH V6 2/2] libxl/arm: Add handling of 
extended regions for DomU"):
> On Mon, 11 Oct 2021, Oleksandr Tyshchenko wrote:
> > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > 
> > The extended region (safe range) is a region of guest physical
> > address space which is unused and could be safely used to create
> > grant/foreign mappings instead of wasting real RAM pages from
> > the domain memory for establishing these mappings.
> > 
> > The extended regions are chosen at the domain creation time and
> > advertised to it via "reg" property under hypervisor node in
> > the guest device-tree. As region 0 is reserved for grant table
> > space (always present), the indexes for extended regions are 1...N.
> > If extended regions could not be allocated for some reason,
> > Xen doesn't fail and behaves as usual, so only inserts region 0.
> > 
> > Please note the following limitations:
> > - The extended region feature is only supported for 64-bit domain
> >   currently.
> > - The ACPI case is not covered.
> > 
> > ***
> > 
> > The algorithm to choose extended regions for non-direct mapped
> > DomU is simpler in comparison with the algorithm for direct mapped
> > Dom0. We usually have a lot of unused space above 4GB, and might
> > have some unused space below 4GB (depends on guest memory size).
> > Try to allocate separate 2MB-aligned extended regions from the first
> > (below 4GB) and second (above 4GB) RAM banks taking into the account
> > the maximum supported guest physical address space size and the amount
> > of memory assigned to the guest. The minimum size of extended region
> > the same as for Dom0 (64MB).
> > 
> > Suggested-by: Julien Grall <jgrall@xxxxxxxxxx>
> > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

On the basis of that and the diffstat:

Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>