[PATCH V3 0/3] Add handling of extended regions (safe ranges) on Arm (Was "xen/memory: Introduce a hypercall to provide unallocated space")

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

You can find an initial discussion at [1],[2] and [3].

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
(the indexes for extended regions are 1...N).
No device tree bindings update is needed, guest infers the presense of extended
regions from the number of regions in "reg" property.
New compatible/property will be needed (but only after this patch [4] or 
alternative
goes in) to indicate that "region 0 is safe to use". Until this patch is merged 
it is
not safe to use extended regions for the grant table space.

The extended regions are calculated differently for direct mapped
Dom0 (with and without IOMMU) and non-direct mapped DomUs.

Please note the following limitations:
- The extended region feature is only supported for 64-bit domain currently.
- The ACPI case is not covered.

Xen patch series is also available at [5]. The corresponding Linux patch series 
is at [6] for now
(last 4 patches).

Tested on Renesas Salvator-X board + H3 ES3.0 SoC (Arm64) with updated 
virtio-disk backend [7]
running in Dom0 (256MB RAM) and DomD (2GB RAM). In both cases the backend 
pre-maps DomU memory
which is 3GB. All foreign memory gets mapped into extended regions (so the 
amount of RAM in
the backend domain is not reduced). No issues were observed.

[1] 
https://lore.kernel.org/xen-devel/1627489110-25633-1-git-send-email-olekstysh@xxxxxxxxx/
[2] 
https://lore.kernel.org/xen-devel/1631034578-12598-1-git-send-email-olekstysh@xxxxxxxxx/
[3] 
https://lore.kernel.org/xen-devel/1631297924-8658-1-git-send-email-olekstysh@xxxxxxxxx/
[4] 
https://lore.kernel.org/xen-devel/1632425551-18910-1-git-send-email-olekstysh@xxxxxxxxx/
[5] https://github.com/otyshchenko1/xen/commits/map_opt_ml4
[6] https://github.com/otyshchenko1/linux/commits/map_opt_ml3
[7] https://github.com/otyshchenko1/virtio-disk/commits/map_opt_next

Oleksandr Tyshchenko (3):
  xen: Introduce "gpaddr_bits" field to XEN_SYSCTL_physinfo
  xen/arm: Add handling of extended regions for Dom0
  libxl/arm: Add handling of extended regions for DomU

 docs/misc/xen-command-line.pandoc |   7 +
 tools/include/libxl.h             |   7 +
 tools/libs/light/libxl.c          |   2 +
 tools/libs/light/libxl_arm.c      |  70 +++++++++-
 tools/libs/light/libxl_types.idl  |   2 +
 xen/arch/arm/domain_build.c       | 280 +++++++++++++++++++++++++++++++++++++-
 xen/arch/arm/sysctl.c             |   2 +
 xen/arch/x86/sysctl.c             |   2 +
 xen/include/public/arch-arm.h     |   3 +
 xen/include/public/sysctl.h       |   4 +-
 10 files changed, 370 insertions(+), 9 deletions(-)

-- 
2.7.4