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Re: [PATCH V7 0/2] Add handling of extended regions (safe ranges) on Arm (Was "xen/memory: Introduce a hypercall to provide unallocated space")

Hello all

On 14.10.21 14:40, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

You can find an initial discussion at [1]-[7].

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 
of wasting real RAM pages from the domain memory for establishing these 

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 [8] or 
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.

Please note that support for Dom0 was already committed, so these patches are 
remaining DomU bits.

Xen patch series is also available at [9]. The corresponding Linux patch series 
is at [10]
for now (last 4 patches).

So, all Xen changes are already committed (thanks!) and I will start trying to push Linux changes. I believe that with your help in review, it will be possible to finish this enabling work.



Oleksandr Tyshchenko



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