Re: [PATCH v3 09/11] KVM: arm64: Introduce KVM_VM_TYPE_ARM_SW_PROTECTED machine type

[Quentin Perret <qperret@google.com>]

Hi Fuad,

On Tuesday 11 Feb 2025 at 12:11:25 (+0000), Fuad Tabba wrote:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 117937a895da..f155d3781e08 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -652,6 +652,12 @@ struct kvm_enable_cap {
>  #define KVM_VM_TYPE_ARM_IPA_SIZE_MASK	0xffULL
>  #define KVM_VM_TYPE_ARM_IPA_SIZE(x)		\
>  	((x) & KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> +
> +#define KVM_VM_TYPE_ARM_SW_PROTECTED	(1UL << 9)

FWIW, the downstream Android code has used bit 31 since forever
for that.

Although I very much believe that upstream should not care about the
downstream mess in general, in this particular instance bit 9 really
isn't superior in any way, and there's a bunch of existing userspace
code that uses bit 31 today as we speak. It is very much Android's
problem to update these userspace programs if we do go with bit 9
upstream, but I don't really see how that would benefit upstream
either.

So, given that there is no maintenance cost for upstream to use bit 31
instead of 9, I'd vote for using bit 31 and ease the landing with
existing userspace code, unless folks are really opinionated with this
stuff :)

Thanks,
Quentin

> +#define KVM_VM_TYPE_MASK	(KVM_VM_TYPE_ARM_IPA_SIZE_MASK | \
> +				 KVM_VM_TYPE_ARM_SW_PROTECTED)
> +
>  /*
>   * ioctls for /dev/kvm fds:
>   */
> -- 
> 2.48.1.502.g6dc24dfdaf-goog
>