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

[Jianyong Wu]

> -----Original Message-----
> From: Marc Zyngier <maz@xxxxxxxxxx>
> Sent: Monday, September 7, 2020 5:47 PM
> To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; sean.j.christopherson@xxxxxxxxx;
> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
> will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Steven Price
> <Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Justin He
> <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
> 
> 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?

Sorry, I should have changed this code according to Will's patch. Thanks for reminder!

Thanks
jianyong
> 
>          M.
> --
> Jazz is not dead. It just smells funny...