Messages in this thread | | | From | "Jianyong Wu (Arm Technology China)" <> | Subject | RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm. | Date | Wed, 9 Oct 2019 05:21:13 +0000 |
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Hi Paolo,
> -----Original Message----- > From: Paolo Bonzini <pbonzini@redhat.com> > Sent: Thursday, September 19, 2019 8:13 PM > To: Marc Zyngier <maz@kernel.org>; Jianyong Wu (Arm Technology China) > <Jianyong.Wu@arm.com>; netdev@vger.kernel.org; yangbo.lu@nxp.com; > john.stultz@linaro.org; tglx@linutronix.de; sean.j.christopherson@intel.com; > richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>; Will > Deacon <Will.Deacon@arm.com>; Suzuki Poulose > <Suzuki.Poulose@arm.com> > Cc: linux-kernel@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>; linux-arm- > kernel@lists.infradead.org > Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm. > > On 19/09/19 13:39, Marc Zyngier wrote: > >> I don't think it's ugly but more important, using tk->tkr_mono.clock > >> is incorrect. See how the x86 code hardcodes &kvm_clock, it's the > >> same for ARM. > > Not really. The guest kernel is free to use any clocksource it wishes. > > Understood, in fact it's the same on x86. > > However, for PTP to work, the cycles value returned by the clocksource must > match the one returned by the hypercall. So for ARM > get_device_system_crosststamp must receive the arch timer clocksource, so > that it will return -ENODEV if the active clocksource is anything else. > As ptp_kvm clock has fixed to arm arch system counter in patch set v4, we need check if the current clocksource is system counter when return clock cycle in host, so a helper needed to return the current clocksource. Could I add this helper in next patch set?
Thanks Jianyong wu
> Paolo > > > In some cases, it is actually desirable (like these broken systems > > that cannot use an in-kernel irqchip...). Maybe it is that on x86 the > > guest only uses the kvm_clock, but that's a much harder sell on ARM. > > The fact that ptp_kvm assumes that the clocksource is fixed doesn't > > seem correct in that case.
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