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

[Cornelia Huck]

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?

>
> Signed-off-by: Jianyong Wu <jianyong.wu@xxxxxxx>
> ---
>  Documentation/virt/kvm/api.rst | 3 ++-
>  arch/arm64/kvm/arm.c           | 1 +
>  include/uapi/linux/kvm.h       | 1 +
>  3 files changed, 4 insertions(+), 1 deletion(-)
>