Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64

[Marc Zyngier]

On 2020-09-07 10:28, Jianyong Wu wrote:
> > -----Original Message-----
> > From: Marc Zyngier <maz@xxxxxxxxxx>
> > Sent: Monday, September 7, 2020 4:55 PM
> > To: Jianyong Wu <Jianyong.Wu@xxxxxxx>

[...]

> > >> 	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_FEATUR
> > >> ES_FUNC_ID,
> > >> > +			     &hvc_res);
> > >> > +	if (!(hvc_res.a0 | BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP)))
> > >> > +		return -EOPNOTSUPP;
> > >> > +
> > >> > +	return 0;
> > >>
> > >> What happens if the
> > >> ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID function isn't
> > implemented
> > >> (on an old kernel or a non-KVM hypervisor)? The expected behaviour is
> > >> that a0 will contain SMCCC_RET_NOT_SUPPORTED, which is -1.
> > >> The result is that this function always returns "supported". Not an
> > >> acceptable behaviour.
> > >>
> > > Oh!  it's really a stupid mistake, should be "&" not "|".
> >
> > But even then. (-1 & whatever) is always true.
>
> Yeah, what about checking if a0 is non-negative first? Like:
> if (hvc_res.a0 < 0 || !(hvc_res.a0 & BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP)))
> 	return -EOPNOTSUPP;

I don't get it. You already carry a patch from Will that gives
you a way to check for a service (kvm_arm_hyp_service_available()).

Why do you need to reinvent the wheel?

        M.
--
Jazz is not dead. It just smells funny...