Re: [PATCH 09/12] xen/arm: if is_domain_direct_mapped use native addresses for GICv3

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 15 Apr 2020, Julien Grall wrote:
> > diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
> > index 4e60ba15cc..4cf430f865 100644
> > --- a/xen/arch/arm/vgic-v3.c
> > +++ b/xen/arch/arm/vgic-v3.c
> > @@ -1677,13 +1677,25 @@ static int vgic_v3_domain_init(struct domain *d)
> 
> 
> I think you also want to modify vgic_v3_max_rdist_count().

I don't think so: domUs even direct-mapped still only get 1 rdist
region. This patch is not changing the layout of the domU gic, it is
only finding a "hole" in the physical address space to make sure there
are no conflicts (or at least minimize the chance of conflicts.)


> >        * Domain 0 gets the hardware address.
> >        * Guests get the virtual platform layout.
> 
> This comment needs to be updated.

Yep, I'll do


> >        */
> > -    if ( is_hardware_domain(d) )
> > +    if ( is_domain_direct_mapped(d) )
> >       {
> >           unsigned int first_cpu = 0;
> > +        unsigned int nr_rdist_regions;
> >             d->arch.vgic.dbase = vgic_v3_hw.dbase;
> >   -        for ( i = 0; i < vgic_v3_hw.nr_rdist_regions; i++ )
> > +        if ( is_hardware_domain(d) )
> > +        {
> > +            nr_rdist_regions = vgic_v3_hw.nr_rdist_regions;
> > +            d->arch.vgic.intid_bits = vgic_v3_hw.intid_bits;
> > +        }
> > +        else
> > +        {
> > +            nr_rdist_regions = 1;
> 
> What does promise your the rdist region will be big enough to cater all the
> re-distributors for your domain?

Good point. I'll add an explicit check for that with at least a warning.
I don't think we want to return error because the configuration it is
still likely to work. 

It might be better to continue this conversation on the next version of
the patch -- it is going to be much clearer.