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

["Jianyong Wu (Arm Technology China)" <Jianyong.Wu@arm.com>]

Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@redhat.com>
> Sent: Wednesday, October 9, 2019 2:36 PM
> To: Jianyong Wu (Arm Technology China) <Jianyong.Wu@arm.com>; Marc
> Zyngier <maz@kernel.org>; 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 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.

Thanks
Jianyong  Wu

> Paolo