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SubjectRE: [RFC PATCH v9 6/8] psci: Add hvc call service for ptp_kvm.
Date
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, January 13, 2020 7:16 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Kaly Xin
> <Kaly.Xin@arm.com>; Justin He <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [RFC PATCH v9 6/8] psci: Add hvc call service for ptp_kvm.
>
> Hi Jianyong,
>
> On 2020-01-13 10:30, Jianyong Wu wrote:
> > Hi Marc,
> >
> >> -----Original Message-----
> >> From: Marc Zyngier <maz@kernel.org>
> >> Sent: Friday, January 10, 2020 6:56 PM NV breaks that assumtion,
> >> because the guest hypervisor is using the physical counter. Also,
> >> let's not forget that the hypercall isn't Linux specific.
> >> I can write my own non-Linux guest and still use this hypercall.
> >> Nothing in
> >> there says that I can't use the physical counter if I want to.
> >>
> >> So somehow, you need to convey the the hypervisor the notion of
> >> *which*
> >> counter the guest uses.
> >>
> >> Does it make sense? Or am I missing something?
> >>
> > I know what you say. Let me try to solve this problem.
> > Step 0, summary out all the conditions we should process, which will
> > sever as branch condition.(now only normal virt and nested virt, I
> > think)
>
> No. You shouldn't think of the various use cases, but of which time
> references a guest can use. You don't need nested virt to use the physical
> counter, for example.
Ok,

>
> > Step 1, figure out the set of reference counter value used by guest
> > in all condition.
>
> That should be for the guest to tell you when it calls into the PV service.
>
Yeah

> > Step 2, determine which reference counter value will be used by
> guest
> > in a certain condition in hypercall.
> > In step 1, can we give the set only 2 elements that one is physical
> > counter the other is virtual counter?
>
> I don't think returning the two values is useful. Just return what the guest
> asks for.
>
> > For step 2, I have no idea for that now. can you give me some hint
> > about it?
>
> Just expand your SMC call to take a parameter indicating the reference
> counter, and return the sampled (or computed) value corresponding to that
> counter.
Get it, I'll try it.

Thanks
Jianyong

>
> M.
> --
> Jazz is not dead. It just smells funny...

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