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From: Marc Zyngier <maz@kernel.org>
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
Date: Mon, 07 Sep 2020 10:47:01 +0100	[thread overview]
Message-ID: <67f3381467d02c8d3f25682cd99898e9@kernel.org> (raw)
In-Reply-To: <HE1PR0802MB25551446DC85DB3684D09211F4280@HE1PR0802MB2555.eurprd08.prod.outlook.com>

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>

[...]

>> >> 	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...

  reply	other threads:[~2020-09-07  9:47 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04  9:27 [PATCH v14 00/10] Enable ptp_kvm for arm64 Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 01/10] arm64: Probe for the presence of KVM hypervisor services during boot Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 02/10] arm/arm64: KVM: Advertise KVM UID to guests via SMCCC Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 03/10] smccc: Export smccc conduit get helper Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 04/10] ptp: Reorganize ptp_kvm module to make it arch-independent Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 05/10] time: Add mechanism to recognize clocksource in time_get_snapshot Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 06/10] clocksource: Add clocksource id for arm arch counter Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 07/10] arm64/kvm: Add hypercall service for kvm ptp Jianyong Wu
2020-09-04 16:15   ` Marc Zyngier
2020-09-07  8:10     ` Jianyong Wu
2020-09-05 11:04   ` Marc Zyngier
2020-09-07  8:13     ` Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 Jianyong Wu
2020-09-05 11:01   ` Marc Zyngier
2020-09-06 10:00     ` Marc Zyngier
2020-09-07  8:40     ` Jianyong Wu
2020-09-07  8:54       ` Marc Zyngier
2020-09-07  9:28         ` Jianyong Wu
2020-09-07  9:47           ` Marc Zyngier [this message]
2020-09-07 10:11             ` Jianyong Wu
2020-09-05 11:33   ` Marc Zyngier
2020-09-07  8:51     ` Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 09/10] doc: add ptp_kvm introduction for arm64 support Jianyong Wu
2020-09-04 16:18   ` Marc Zyngier
2020-09-07  7:55     ` Jianyong Wu
2020-09-04  9:27 ` [PATCH v14 10/10] arm64: Add kvm capability check extension for ptp_kvm Jianyong Wu

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