Re: [XEN PATCH v8 08/22] xen/arm: ffa: add support for FFA_ID_GET

[Julien Grall <julien@xxxxxxx>]

On 13/04/2023 12:07, Henry Wang wrote:
> Hi Jens,
>
> > -----Original Message-----
> > Subject: [XEN PATCH v8 08/22] xen/arm: ffa: add support for FFA_ID_GET
> >
> > Adds support for the FF-A function FFA_ID_GET to return the ID of the
> > calling client.
> >
> > Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> > ---
> >   xen/arch/arm/tee/ffa.c | 21 +++++++++++++++++++++
> >   1 file changed, 21 insertions(+)
> >
> > diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> > index 90ed71cbfda3..f129879c5b81 100644
> > --- a/xen/arch/arm/tee/ffa.c
> > +++ b/xen/arch/arm/tee/ffa.c
> > @@ -181,6 +181,12 @@ static bool ffa_get_version(uint32_t *vers)
> >       return true;
> >   }
> >
> > +static uint16_t get_vm_id(const struct domain *d)
> > +{
> > +    /* +1 since 0 is reserved for the hypervisor in FF-A */
> > +    return d->domain_id + 1;
> Since here you want 0 to be reserved, I think maybe you can use
> the "d->arch.p2m.vmid"? According to the logic in p2m_alloc_vmid(),
> the "d->arch.p2m.vmid" is also a per-domain u16 value that starts
> from 1.
I would rather not do that for a few reasons:
 1) This is assuming the P2M code is initialized first
 2) We should not rely on the VMID to be fixed. We may need to change 
that if we want to run more VMs than the number of VMIDs (we may even 
need multiple VMIDs per domain...).
Cheers,

--
Julien Grall