Re: [PATCH v2 15/21] libs/guest: obtain a compatible cpu policy from two input ones

[Wei Liu <wl@xxxxxxx>]

On Wed, Apr 21, 2021 at 01:26:49PM +0200, Roger Pau Monné wrote:
> On Wed, Apr 21, 2021 at 10:22:39AM +0000, Wei Liu wrote:
> > On Tue, Apr 13, 2021 at 04:01:33PM +0200, Roger Pau Monne wrote:
> > > Introduce a helper to obtain a compatible cpu policy based on two
> > > input cpu policies. Currently this is done by and'ing all CPUID leaves
> > > and MSR entries, except for MSR_ARCH_CAPABILITIES which has the RSBA
> > > bit or'ed.
> > > 
> > 
> > I thought canonical source for compatibility was to be put into the
> > hypervisor, thus all this functionality would be in the hypervisor. Am I
> > misremembering?
> 
> Andrew said something similar on v1, but I'm not able to figure how
> this would be used by the hypervisor.
> 
> It's my understating that the toolstack will attempt to generate a CPU
> policy and forward it to the hypervisor, which will either accept or
> reject it based on the capabilities of the system. I'm not sure I see
> why we would need to give the hypervisor two policies in order to
> generate a resulting compatible one - it should all be done by the
> toolstack AFAICT.
> 
> If there's a use case for this being in the hypervisor I'm happy to
> add it there, but so far I haven't been able to come up with one
> myself, and hence I don't see the need to make the code available.

I have no opinion here. Just wanted to get on the same page.

Thanks for the explanation.

Wei.

> 
> Thanks, Roger.