# Re: \[PATCH v2\] KVM: PPC: Report single stepping capability

- From: Paul Mackerras \<hidden\>
- Date: 2019-06-17 06:18:03 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2019/06/9510372
- Thread: https://ratatoskr.run/kvm/2019/05/9510106/t.md

```text
On Wed, May 29, 2019 at 07:22:19PM -0300, Fabiano Rosas wrote:
> When calling the KVM_SET_GUEST_DEBUG ioctl, userspace might request
> the next instruction to be single stepped via the
> KVM_GUESTDBG_SINGLESTEP control bit of the kvm_guest_debug structure.
> 
> We currently don't have support for guest single stepping implemented
> in Book3S HV.
> 
> This patch adds the KVM_CAP_PPC_GUEST_DEBUG_SSTEP capability in order
> to inform userspace about the state of single stepping support.

Comment/question below:

> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -538,6 +538,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_IMMEDIATE_EXIT:
>  		r = 1;
>  		break;
> +	case KVM_CAP_PPC_GUEST_DEBUG_SSTEP:
> +#ifdef CONFIG_BOOKE
> +		r = 1;
> +		break;
> +#endif

In the !CONFIG_BOOKE case, this will fall through to code which will
return 0 for HV KVM or 1 for PR KVM.  Is that what was intended?
If so, then why do we need the CONFIG_BOOKE case?  Isn't hv_enabled
always 0 on Book E?

In any case, I think this needs at least a /* fall through */ comment
in the code, and something explicit in the patch description to say
that we intend to return 1 on PR KVM.

Paul.
```