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

[Daniel Henrique Barboza <danielhb413@gmail.com>]

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);
>>   }
>>   
>