On Tuesday 20 November 2007, Avi Kivity wrote:
>
> >
> > Sorry for being late in this thread.
> > We (s390) will need a hypercall as we do not have port I/O. I think it
> > should be
> > possible to default to hypercall on s390 and use pio everywhere else.
> >
>
> Or be generic: advertise the methods available according to host
> (kvm/x86, qemu/x86, kvm/s390) and let the guest pick.
Not sure if I'm following the reasoning here. Shouldn't the method be
inherent to the virtio bus driver?
When you use a PCI based virtio bus, the natural choice would be PIO
in some way, but you could also have a different virtio implementation
on PCI that uses hcalls. This choice is completely up to virtio-pci.
On s390, you have a different virtio backend altogether, so you always
use DIAG or hcall instead of whatever virtio-pci does.
The virtio-blk and other high-level drivers don't need to care about
what transport the bus uses in the first place.
Arnd <><
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