RE: [RFC PATCH v9 6/8] psci: Add hvc call service for ptp_kvm.

[Jianyong Wu]

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@xxxxxxxxxx>
> Sent: Monday, January 13, 2020 7:16 PM
> To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
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> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
> will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Steven Price
> <Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
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> kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Kaly Xin
> <Kaly.Xin@xxxxxxx>; Justin He <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
> 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@xxxxxxxxxx>
> >> 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...