netdev - RE: [PATCH v14 08/10] ptp: arm64: Enable ptp

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Date:   Mon, 7 Sep 2020 10:11:31 +0000
From:   Jianyong Wu <Jianyong.Wu@....com>
To:     Marc Zyngier <maz@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "yangbo.lu@....com" <yangbo.lu@....com>,
        "john.stultz@...aro.org" <john.stultz@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        Mark Rutland <Mark.Rutland@....com>,
        "will@...nel.org" <will@...nel.org>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Steven Price <Steven.Price@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Steve Capper <Steve.Capper@....com>,
        Justin He <Justin.He@....com>, nd <nd@....com>
Subject: RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64



> -----Original Message-----
> From: Marc Zyngier <maz@...nel.org>
> Sent: Monday, September 7, 2020 5:47 PM
> To: Jianyong Wu <Jianyong.Wu@....com>
> Cc: netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org;
> tglx@...utronix.de; pbonzini@...hat.com; sean.j.christopherson@...el.com;
> richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>;
> will@...nel.org; Suzuki Poulose <Suzuki.Poulose@....com>; Steven Price
> <Steven.Price@....com>; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; kvmarm@...ts.cs.columbia.edu;
> kvm@...r.kernel.org; Steve Capper <Steve.Capper@....com>; Justin He
> <Justin.He@....com>; nd <nd@....com>
> 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@...nel.org>
> >> Sent: Monday, September 7, 2020 4:55 PM
> >> To: Jianyong Wu <Jianyong.Wu@....com>
> 
> [...]
> 
> >> >> 	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...