[RFC PATCH 2/2] qemu: Add support for max physical address size

[Dario Faggioli]

On Wed, 2020-11-04 at 13:14 +0000, Daniel P. Berrangé wrote:
> On Thu, Oct 29, 2020 at 03:55:42PM +0000, Dario Faggioli wrote:
> > This patch maps /domain/cpu/maxphysaddr into -cpu parameters:
> > 
> >   - <maxphysaddr mode='passthrough'/> becomes host-phys-bits=on
> >   - <maxphysaddr mode='emualte' bits='42'/> becomes phys-bits=42
> > 
> > Passthrough mode can only be used if the chosen CPU model is
> > 'host-passthrough'.
> > 
> > The feature is available since QEMU 2.7.0.
> 
> I wonder if we need to care about doing any kind of host
> compatibility
> checking when these are specified.
> 
Ah, yes, this is a good point.

> QEMU is reluctant to change things due to back compat issues with
> existing deployments. Libvirt wouldn't have that issue though, as
> we would only need to enforce it when users actually gave the
> <maxphysaddr> element, which is opt-in and won't be present in
> existing guests.
> 
Yes, and I'm already adding the logic for checking the host phys bits,
for putting it in the host capabilities, so it should be easy enough to
add a check here.

I'll go for it.

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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