Re: [PATCH] KVM: s390: fix cc for successful PQAP

[Halil Pasic <pasic@linux.ibm.com>]

On Fri,  1 Dec 2023 19:16:57 +0100
Eric Farman <farman@linux.ibm.com> wrote:

> The various errors that are possible when processing a PQAP
> instruction (the absence of a driver hook, an error FROM that
> hook), all correctly set the PSW condition code to 3. But if
> that processing works successfully, CC0 needs to be set to
> convey that everything was fine.
> 
> Fix the check so that the guest can examine the condition code
> to determine whether GPR1 has meaningful data.
> 
> Fixes: e5282de93105 ("s390: ap: kvm: add PQAP interception for AQIC")
> Signed-off-by: Eric Farman <farman@linux.ibm.com>

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

> ---
>  arch/s390/kvm/priv.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 621a17fd1a1b..f875a404a0a0 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -676,8 +676,12 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
>  	if (vcpu->kvm->arch.crypto.pqap_hook) {
>  		pqap_hook = *vcpu->kvm->arch.crypto.pqap_hook;
>  		ret = pqap_hook(vcpu);
> -		if (!ret && vcpu->run->s.regs.gprs[1] & 0x00ff0000)
> -			kvm_s390_set_psw_cc(vcpu, 3);

Maybe a comment that tells pqap_hook() returns 0 or -EOPNOTSUPP
that singnals this should be handled by QEMU. But that can certainly
be done on top, and it is not a part of a minimal fix.

> +		if (!ret) {
> +			if (vcpu->run->s.regs.gprs[1] & 0x00ff0000)
> +				kvm_s390_set_psw_cc(vcpu, 3);
> +			else
> +				kvm_s390_set_psw_cc(vcpu, 0);
> +		}
>  		up_read(&vcpu->kvm->arch.crypto.pqap_hook_rwsem);
>  		return ret;
>  	}