[RFC PATCH 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].

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 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.
- The ACPI case is not covered.

Also please note that we haven't figured out yet how to properly 
extend the Xen hypervisor device-tree bindings on Arm (either via new
compatible or via new property). I decided to go with new property
for now, but this can be changed. This uncertainty is the main reason
why this series is marked as RFC.

Patch series is also available at [2].

The corresponding Linux changes is not in a good shape now (require
some cleanup and refactoring), I will publish them once put them
in order (I hope, it will be in a few days).

[1] 
https://lore.kernel.org/xen-devel/1627489110-25633-1-git-send-email-olekstysh@xxxxxxxxx/
[2] https://github.com/otyshchenko1/xen/commits/map_opt_ml2

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

 tools/include/libxl.h            |   7 ++
 tools/libs/light/libxl.c         |   2 +
 tools/libs/light/libxl_arm.c     |  92 +++++++++++++++-
 tools/libs/light/libxl_types.idl |   2 +
 xen/arch/arm/domain_build.c      | 233 ++++++++++++++++++++++++++++++++++++++-
 xen/arch/arm/sysctl.c            |   2 +
 xen/arch/x86/sysctl.c            |   2 +
 xen/include/public/sysctl.h      |   3 +-
 8 files changed, 338 insertions(+), 5 deletions(-)

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2.7.4