Hi Paolo, > -----Original Message----- > From: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Sent: Thursday, September 19, 2019 8:13 PM > To: Marc Zyngier <maz@xxxxxxxxxx>; Jianyong Wu (Arm Technology China) > <Jianyong.Wu@xxxxxxx>; netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; > john.stultz@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; sean.j.christopherson@xxxxxxxxx; > richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>; Will > Deacon <Will.Deacon@xxxxxxx>; Suzuki Poulose > <Suzuki.Poulose@xxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Steve Capper > <Steve.Capper@xxxxxxx>; Kaly Xin (Arm Technology China) > <Kaly.Xin@xxxxxxx>; Justin He (Arm Technology China) > <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>; linux-arm- > kernel@xxxxxxxxxxxxxxxxxxx > 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.
