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

[Oleksandr <olekstysh@xxxxxxxxx>]

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
> > patch.
> 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.
>
> Thanks,
> Ian.
--
Regards,

Oleksandr Tyshchenko