RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.

[Jianyong Wu (Arm Technology China)]

Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonz...@redhat.com>
> Sent: Wednesday, October 9, 2019 5:13 PM
> To: Jianyong Wu (Arm Technology China) <jianyong...@arm.com>; Marc
> Zyngier <m...@kernel.org>; net...@vger.kernel.org; yangbo...@nxp.com;
> john.stu...@linaro.org; t...@linutronix.de; sean.j.christopher...@intel.com;
> richardcoch...@gmail.com; Mark Rutland <mark.rutl...@arm.com>; Will
> Deacon <will.dea...@arm.com>; Suzuki Poulose
> <suzuki.poul...@arm.com>
> Cc: linux-kernel@vger.kernel.org; k...@vger.kernel.org; Steve Capper
> <steve.cap...@arm.com>; Kaly Xin (Arm Technology China)
> <kaly....@arm.com>; Justin He (Arm Technology China)
> <justin...@arm.com>; nd <n...@arm.com>; linux-arm-
> ker...@lists.infradead.org
> Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
> 
> On 09/10/19 10:18, Jianyong Wu (Arm Technology China) wrote:
> > Hi Paolo,
> >
> >> -----Original Message-----
> >> From: Paolo Bonzini <pbonz...@redhat.com>
> >> Sent: Wednesday, October 9, 2019 2:36 PM
> >> To: Jianyong Wu (Arm Technology China) <jianyong...@arm.com>; Marc
> >> Zyngier <m...@kernel.org>; net...@vger.kernel.org;
> yangbo...@nxp.com;
> >> john.stu...@linaro.org; t...@linutronix.de;
> >> sean.j.christopher...@intel.com; richardcoch...@gmail.com; Mark
> >> Rutland <mark.rutl...@arm.com>; Will Deacon
> <will.dea...@arm.com>;
> >> Suzuki Poulose <suzuki.poul...@arm.com>
> >> Cc: linux-kernel@vger.kernel.org; k...@vger.kernel.org; Steve Capper
> >> <steve.cap...@arm.com>; Kaly Xin (Arm Technology China)
> >> <kaly....@arm.com>; Justin He (Arm Technology China)
> >> <justin...@arm.com>; nd <n...@arm.com>; linux-arm-
> >> ker...@lists.infradead.org
> >> Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
> >>
> >> On 09/10/19 07:21, Jianyong Wu (Arm Technology China) wrote:
> >>> 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?
> >>
> >> You don't need a helper.  You need to return the ARM arch counter
> >> clocksource in the struct system_counterval_t that you return.
> >> get_device_system_crosststamp will then check that the clocksource
> >> matches the active one.
> >
> > We must ensure both of the host and guest using the same clocksource.
> > get_device_system_crosststamp will check the clocksource of guest and
> > we also need check the clocksource in host, and struct type can't be
> transferred from host to guest using arm hypercall.
> > now we lack of a mechanism to check the current clocksource. I think this
> will be useful if we add one.
> 
> Got it---yes, I think adding a struct clocksource to struct
> system_time_snapshot would make sense.  Then the hypercall can just use
> ktime_get_snapshot and fail if the clocksource is not the ARM arch counter.
> 
> John (Stultz), does that sound good to you?  The context is that Jianyong
> would like to add a hypercall that returns a (cycles,
> nanoseconds) pair to the guest.  On x86 we're relying on the vclock_mode
> field that is already there for the vDSO, but being able to just use
> ktime_get_snapshot would be much nicer.
> 

Could I add struct clocksource to system_time_snapshot struct in next version 
of my patch set?

Jianyong Wu
Thanks

> Paolo