Re: [PATCH V4 23/24] libxl: Introduce basic virtio-mmio support on Arm

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 20 Jan 2021, Julien Grall wrote:
> > > > +#define GUEST_VIRTIO_MMIO_SIZE xen_mk_ullong(0x200)
> > > 
> > > AFAICT, the size of the virtio mmio region should be 0x100. So why is it
> > > 0x200?
> > 
> > 
> > I didn't find the total size requirement for the mmio region in virtio
> > specification v1.1 (the size of control registers is indeed 0x100 and
> > device-specific configuration registers starts at the offset 0x100, however
> > it's size depends on the device and the driver).
> > 
> > kvmtool uses 0x200 [1], in some Linux device-trees we can see 0x200 [2]
> > (however, device-tree bindings example has 0x100 [3]), so what would be the
> > proper value for Xen code?
> 
> Hmm... I missed that fact. I would say we want to use the biggest size
> possible so we can cover most of the devices.
> 
> Although, as you pointed out, this may not cover all the devices. So maybe we
> want to allow the user to configure the size via xl.cfg for the one not
> conforming with 0x200.
> 
> This could be implemented in the future. Stefano/Ian, what do you think?

I agree it could be implemented in the future. For now, I would pick
0x200.