Re: [RFC PATCH 3/8] spapr_numa.c: wait for CAS before writing rtas DT

[Daniel Henrique Barboza]

On 6/15/21 1:02 AM, David Gibson wrote:
> On Mon, Jun 14, 2021 at 10:33:04PM -0300, Daniel Henrique Barboza wrote:
> > spapr_numa_write_rtas_dt() is called from spapr_dt_rtas(), which in
> > turned is called by spapr_build_fdt(). spapr_build_fdt() is called in
> > two places: spapr_machine_reset() and do_client_architecture_support().
> > When called in machine_reset() we're writing RTAS nodes with NUMA
> > artifacts without going through CAS first.
> >
> > This is not an issue because we always write the same thing in DT, since
> > we support just FORM1 NUMA affinity. With the upcoming FORM2 support,
> > we're now reliant on guest choice to decide what to write.
> >
> > Instead of taking a guess (e.g. default to FORM1, switch to FORM2 if
> > guest chooses it), postpone the writing of
> > ibm,associativity-reference-points and ibm,max-associativity-domains
> > until we're sure what was negotiated with the guest.
> >
> > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>
> I think it makes sense to fold this in with 1/8 moving the calculation
> itself until after CAS.

Ok.

> This does make a (theoretical) functional change - it means that NUMA
> information is not available before CAS, which it was before.  I think
> that's very unlikely to break anything, but I wonder if we should make
> it dependent on the machine version just to be safe.

I don't mind making it dependent on the default machine. I'll wrap this
CAS change (and as result, all FORM2 support) to be available only for
the default machine type.


Thanks,


Daniel

> > ---
> >   hw/ppc/spapr_numa.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
> > index 04a86f9b5b..e1a7f80076 100644
> > --- a/hw/ppc/spapr_numa.c
> > +++ b/hw/ppc/spapr_numa.c
> > @@ -379,6 +379,10 @@ static void 
> > spapr_numa_FORM1_write_rtas_dt(SpaprMachineState *spapr,
> >    */
> >   void spapr_numa_write_rtas_dt(SpaprMachineState *spapr, void *fdt, int rtas)
> >   {
> > +    if (spapr_ovec_empty(spapr->ov5_cas)) {
> > +        return;
> > +    }
> > +
> >       spapr_numa_FORM1_write_rtas_dt(spapr, fdt, rtas);
> >   }
> >