Re: [Xen-devel] [PATCH v3 5/6] xen/arm: introduce nr_spis

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 9 Aug 2019, Julien Grall wrote:
> Hi Stefano,
> 
> On 8/9/19 12:12 AM, Stefano Stabellini wrote:
> > We don't have a clear way to know how many virtual SPIs we need for the
> > boot domains. Introduce a new option under xen,domain to specify the
> > number of SPIs to allocate for the domain.
> > 
> > The property is optional, when absent, we'll use the physical number of
> > gic lines for dom0less domains, just like for dom0. Given that dom0less
> > VMs are meant for static partitioning scenarios where the number of VMs
> > is very low, increased memory overhead should not be a problem, and it
> > is possible to minimizing it by using "nr_spis".
> > 
> > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > ---
> > Changes in v3:
> > - improve commit message
> > - introduce nr_spis
> > ---
> >   xen/arch/arm/domain_build.c | 7 +++----
> >   1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index 0057a509d1..fc4e5bc4ca 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -2270,7 +2270,6 @@ void __init create_domUs(void)
> >           struct domain *d;
> >           struct xen_domctl_createdomain d_cfg = {
> >               .arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE,
> > -            .arch.nr_spis = 0,
> >               .flags = XEN_DOMCTL_CDF_hvm_guest | XEN_DOMCTL_CDF_hap,
> >               .max_evtchn_port = -1,
> >               .max_grant_frames = 64,
> > @@ -2280,13 +2279,13 @@ void __init create_domUs(void)
> >           if ( !dt_device_is_compatible(node, "xen,domain") )
> >               continue;
> >   -        if ( dt_property_read_bool(node, "vpl011") )
> > -            d_cfg.arch.nr_spis = GUEST_VPL011_SPI - 32 + 1;
> > -
> 
> This change is not specified in the commit message nor the documentation.

I'll add a reference in the commit message.


> This will likely lead to some issues if the number of SPIs programmed (either
> from the DT or the Hardware) is smaller than the the SPI here.
> 
> Furthemore, it is important to write down in the documentation that the SPI
> used by vpl011 may clash with a device interrupt routed to the guest.

Good points, I'll add those info to the docs.


> >           if ( !dt_property_read_u32(node, "cpus", &d_cfg.max_vcpus) )
> >               panic("Missing property 'cpus' for domain %s\n",
> >                     dt_node_name(node));
> >   +        if ( !dt_property_read_u32(node, "nr_spis", &d_cfg.arch.nr_spis)
> > )
> > +            d_cfg.arch.nr_spis = gic_number_lines() - 32;
> > +
> >           d = domain_create(++max_init_domid, &d_cfg, false);
> >           if ( IS_ERR(d) )
> >               panic("Error creating domain %s\n", dt_node_name(node));
> > 
> 
> Cheers,
> 
> -- 
> Julien Grall
> 

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