Re: [PATCH V3 3/3] libxl/arm: Add handling of extended regions for DomU

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi,

On 24.09.2021 00:48, 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. As we have a lot of unused space above 4GB, provide single
> 2MB-aligned region from the second RAM bank taking into the account
> the maximum supported guest address space size and the amount of
> memory assigned to the guest. The maximum size of the region is 128GB.
> The minimum size is 64MB.
> 
> Suggested-by: Julien Grall <jgrall@xxxxxxxxxx>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> ---
> Changes RFC -> V2:
>    - update patch description
>    - drop uneeded "extended-region" DT property
>    - clear reg array in finalise_ext_region() and add a TODO
> 
> Changes V2 -> V3:
>    - update patch description, comments in code
>    - only pick up regions with size >= 64MB
>    - move the region calculation to make_hypervisor_node() and drop
>      finalise_ext_region()
>    - extend the list of arguments for make_hypervisor_node()
>    - do not show warning for 32-bit domain
>    - change the region alignment from 1GB to 2MB
>    - move EXT_REGION_SIZE to public/arch-arm.h
> ---
>  tools/libs/light/libxl_arm.c  | 70 
> +++++++++++++++++++++++++++++++++++++++----
>  xen/include/public/arch-arm.h |  3 ++
>  2 files changed, 68 insertions(+), 5 deletions(-)
> 
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
Tested-by: Michal Orzel <michal.orzel@xxxxxxx>

Cheers