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From:   Jianyong Wu <Jianyong.Wu@arm.com>
To:     Marc Zyngier <maz@kernel.org>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "yangbo.lu@nxp.com" <yangbo.lu@nxp.com>,
        "john.stultz@linaro.org" <john.stultz@linaro.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "sean.j.christopherson@intel.com" <sean.j.christopherson@intel.com>,
        "richardcochran@gmail.com" <richardcochran@gmail.com>,
        Mark Rutland <Mark.Rutland@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Steven Price <Steven.Price@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Steve Capper <Steve.Capper@arm.com>,
        Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
Thread-Topic: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
Thread-Index: AQHWgp4Q48WtGxJp4kuFSJTL6o01LqlZ4qMAgAL3/tCAAAlCgIAABDCQgAAKXICAAAXbMA==
Date:   Mon, 7 Sep 2020 10:11:31 +0000
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> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, September 7, 2020 5:47 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He
> <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
>=20
> On 2020-09-07 10:28, Jianyong Wu wrote:
> >> -----Original Message-----
> >> From: Marc Zyngier <maz@kernel.org>
> >> Sent: Monday, September 7, 2020 4:55 PM
> >> To: Jianyong Wu <Jianyong.Wu@arm.com>
>=20
> [...]
>=20
> >> >> 	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;
>=20
> 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()).
>=20
> Why do you need to reinvent the wheel?

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

Thanks
jianyong
>=20
>          M.
> --
> Jazz is not dead. It just smells funny...