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

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 2086 bytes --]

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.

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.

> ---
>  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);
>  }
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]