Re: [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter

[Marc Zyngier]

On Thu, 16 Nov 2023 13:08:58 +0000,
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
> 
> On Thu, Nov 16 2023, Jianyong Wu <jianyong.wu@xxxxxxx> wrote:
> 
> > 821d935c87b introduces support for userspace SMCCC filtering, but lack
> > of a way to tell userspace if we have this feature. Add a corresponding
> > feature extension can resolve this issue.
> >
> > For example, the incoming feature Vcpu Hotplug needs the SMCCC filter.
> > As there is no way to check this feature, VMM will run into error when
> > it calls this feature on an old kernel. It's bad for backward compatible.
> 
> Can't you simply query via KVM_HAS_DEVICE_ATTR whether the SMCCC
> filtering controls exist?

Quite. Commit e0fc6b21616dd introduced it for that exact purpose,
specifically to prevent adding more of these capabilities when there
is a corresponding attribute that can be readily queried.

	M.

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