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

[Marc Zyngier]

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.

> 	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.

> 	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.

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