Re: [RFC 2/9] target/arm: parse cpu feature related options

[Andrew Jones]

On Sat, Aug 15, 2020 at 10:19:12AM +0800, Peng Liang wrote:
> On 8/13/2020 8:21 PM, Andrew Jones wrote:
> > On Thu, Aug 13, 2020 at 06:26:50PM +0800, Peng Liang wrote:
> >> The implementation of CPUClass::parse_features only supports CPU
> >> features in "feature=value" format.  However, libvirt maybe send us a
> >> CPU feature string in "+feature/-feature" format. 
> > 
> > Why would libvirt do that? If we have a boolean feature, then I'd think
> > libvirt should be capable of sending feature=on/off just as easily as a
> > +/-feature. Indeed libvirt seems to do the right thing with all the
> > CPU features we already have: pmu, sve*, ...
> > 
> > Thanks,
> > drew
> > 
> > .
> > 
> 
> Libvirt before d47db7b16dd5422c7e487c8c8ee5b181a2f9cd66 ("qemu: command:
> Support new cpu feature argument syntax") will send +/-feature.  Does QEMU
> need to support it?  If not, I'll remote it.

No, we don't need to support pre-2016 libvirt, at least not for ARM CPU
features, because libvirt didn't start querying QEMU for ARM CPU features
until just last year.

Thanks,
drew