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Re: [PATCH V6 1/2] xen/arm: Introduce gpaddr_bits field to struct xen_domctl_getdomaininfo

On 12.10.21 18:15, Ian Jackson wrote:

Hi Ian

Oleksandr Tyshchenko writes ("[PATCH V6 1/2] xen/arm: Introduce gpaddr_bits field to 
struct xen_domctl_getdomaininfo"):
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

We need to pass info about maximum supported guest physical
address space size to the toolstack on Arm in order to properly
calculate the base and size of the extended region (safe range)
for the guest. The extended region is unused address space which
could be safely used by domain for foreign/grant mappings on Arm.
The extended region itself will be handled by the subsequent
You say "to the toolstack", but you are exposing this information up
to callers of libxl.  Do you mean some higher-layer toolstack that
uses libxl ?  What does it use this information for ?

FTAOD I am not opposed to exposing this in this way; indeed it seems
likely to be useful.  I just want to fully understand before I give
this my tools ack.
I didn't mean any higher-layer toolstack, sorry if I was unclear. In the first place this information is needed by the entity which generates the device-tree for the guest on Arm (tools/libs/light/libxl_arm.c) to properly calculate the extended regions to be inserted into the hypervisor node.

+        info->gpaddr_bits = domctl.u.getdomaininfo.gpaddr_bits;
I'm pleased to find that this is not arch-specific.



Oleksandr Tyshchenko



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