Re: [PATCH v2 2/5] KVM: arm64: Get rid of host SVE tracking/saving

Marc Zyngier
2021-11-22T18:10:34Z

On Mon, 22 Nov 2021 17:58:00 +0000,
Mark Brown <broonie@kernel.org> wrote:
>
> On Mon, Nov 22, 2021 at 03:57:32PM +0000, Marc Zyngier wrote:
> > Zenghui Yu <yuzenghui@huawei.com> wrote:
>
> > > Nit: This removes the only user of __sve_save_state() helper. Should we
> > > still keep it in fpsimd.S?
>
> > I was in two minds about that, as I'd like to eventually be able to
> > use SVE for protected guests, where the hypervisor itself has to be in
> > charge of the FP/SVE save-restore.
>
> > But that's probably several months away, and I can always revert a
> > deletion patch if I need to, so let's get rid of it now.
>
> While we're on the subject of potential future work we might in future
> want to not disable SVE on every syscall if (as seems likely) it turns
> out that that's more performant for small vector lengths

[...]

How are you going to retrofit that into userspace? This would be an
ABI change, and I'm not sure how you'd want to deal with that
transition...

M.

--
Without deviation from the norm, progress is not possible.