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

From: Daniel Henrique Barboza
Subject: Re: [RFC PATCH 3/8] spapr_numa.c: wait for CAS before writing rtas DT
Date: Tue, 15 Jun 2021 17:26:29 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1

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.


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.



  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);

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