From: Thomas Gleixner <tglx@linutronix.de>
To: "Jianyong Wu (Arm Technology China)" <Jianyong.Wu@arm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"yangbo.lu@nxp.com" <yangbo.lu@nxp.com>,
"john.stultz@linaro.org" <john.stultz@linaro.org>,
"sean.j.christopherson@intel.com"
<sean.j.christopherson@intel.com>,
"maz@kernel.org" <maz@kernel.org>,
"richardcochran@gmail.com" <richardcochran@gmail.com>,
Mark Rutland <Mark.Rutland@arm.com>,
"will@kernel.org" <will@kernel.org>,
Suzuki Poulose <Suzuki.Poulose@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>,
"Kaly Xin (Arm Technology China)" <Kaly.Xin@arm.com>,
"Justin He (Arm Technology China)" <Justin.He@arm.com>,
nd <nd@arm.com>
Subject: RE: [PATCH v5 3/6] timekeeping: Add clocksource to system_time_snapshot
Date: Wed, 16 Oct 2019 12:23:37 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1910161218020.2046@nanos.tec.linutronix.de> (raw)
In-Reply-To: <HE1PR0801MB1676EC775B7BFA5FC7E4F9D5F4920@HE1PR0801MB1676.eurprd08.prod.outlook.com>
Jianyong,
On Wed, 16 Oct 2019, Jianyong Wu (Arm Technology China) wrote:
Please fix your mail client not to copy the full headers into the reply.
> > On Wed, 16 Oct 2019, Paolo Bonzini wrote:
> > > On 15/10/19 22:13, Thomas Gleixner wrote:
> > That's a completely different beast, really.
> >
> > The clocksource pointer is handed in by the caller and the core code validates
> > if the clocksource is the same as the current system clocksource and not the
> > other way round.
> >
> > So there is no need for getting that pointer from the core code because the
> > caller knows already which clocksource needs to be active to make.the whole
> > cross device timestamp correlation work. And in that case it's the callers
> > responsibility to ensure that the pointer is valid which is the case for the
> > current use cases.
> >
> I thinks there is something misunderstanding of my patch. See patch 4/6,
> the reason why I add clocksource is that I want to check if the current
> clocksouce is arm_arch_counter in virt/kvm/arm/psci.c and nothing to do
> with get_device_system_crosststamp.
There is no misunderstanding at all. Your patch is broken in several ways
as I explained in detail.
> So I really need a mechanism to do that check.
>
> Thanks
> Jianyong
So just by chance I scrolled further down and found more replies from
you. Please trim the reply properly and add your 'Thanks Jianyong' to the
end of the mail.
> > From your other reply:
> >
> > > Why add a global id? ARM can add it to archdata similar to how x86
> > > has vclock_mode. But I still think the right thing to do is to
> > > include the full system_counterval_t in the result of
> > > ktime_get_snapshot. (More in a second, feel free to reply to the other
> > email only).
> >
> > No, the clocksource pointer is not going to be exposed as there is no
> > guarantee that it will be still around after the call returns.
> >
> > It's not even guaranteed to be correct when the store happens in Wu's patch
> > simply because the store is done outside of the seqcount protected region.
>
> Yeah, all of the elements in system_time_snapshot should be captured in
> consistency. So I think the consistency will be guaranteed if the store
> ops added in the seqcount region.
Again. While it is consistent in terms of storage, it's still wrong to
expose a pointer to something which has no life time guarantee. Even if
your use case is just to compare the pointer it's a bad idea to do that
especially without any comment about the pointer validity at all.
Thanks,
tglx
next prev parent reply other threads:[~2019-10-16 10:23 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-15 10:48 [RFC PATCH v5 0/6] Enable ptp_kvm for arm64 Jianyong Wu
2019-10-15 10:48 ` [PATCH v5 1/6] psci: Export psci_ops.conduit symbol as modules will use it Jianyong Wu
2019-10-15 17:24 ` Mark Rutland
2019-10-16 3:54 ` Jianyong Wu (Arm Technology China)
2019-10-15 10:48 ` [PATCH v5 2/6] ptp: Reorganize ptp_kvm modules to make it arch-independent Jianyong Wu
2019-10-16 7:10 ` Paolo Bonzini
2019-10-16 10:04 ` Jianyong Wu (Arm Technology China)
2019-10-15 10:48 ` [PATCH v5 3/6] timekeeping: Add clocksource to system_time_snapshot Jianyong Wu
2019-10-15 16:37 ` Paolo Bonzini
2019-10-15 20:13 ` Thomas Gleixner
2019-10-15 22:36 ` Paolo Bonzini
2019-10-16 7:28 ` Thomas Gleixner
2019-10-16 9:48 ` Jianyong Wu (Arm Technology China)
2019-10-16 10:23 ` Thomas Gleixner [this message]
2019-10-15 20:12 ` Thomas Gleixner
2019-10-15 22:35 ` Paolo Bonzini
2019-10-16 10:01 ` Jianyong Wu (Arm Technology China)
2019-10-16 10:26 ` Thomas Gleixner
2019-10-15 10:48 ` [PATCH v5 4/6] psci: Add hvc call service for ptp_kvm Jianyong Wu
2019-10-16 7:24 ` Paolo Bonzini
2019-10-16 7:31 ` Thomas Gleixner
2019-10-16 7:42 ` Paolo Bonzini
2019-10-16 10:20 ` Jianyong Wu (Arm Technology China)
2019-10-15 10:48 ` [PATCH v5 5/6] ptp: arm64: Enable ptp_kvm for arm64 Jianyong Wu
2019-10-15 16:39 ` Paolo Bonzini
2019-10-16 3:52 ` Jianyong Wu (Arm Technology China)
2019-10-16 7:10 ` Paolo Bonzini
2019-10-16 7:13 ` Paolo Bonzini
2019-10-16 10:11 ` Jianyong Wu (Arm Technology China)
2019-10-15 10:48 ` [PATCH v5 6/6] kvm: arm64: Add capability check extension for ptp_kvm Jianyong Wu
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