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

[Oleksandr <olekstysh@xxxxxxxxx>]

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 
> 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 [8] 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.
>
> 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.

[snip]

--
Regards,

Oleksandr Tyshchenko