Re: [kvm-unit-tests PATCH v3 4/9] s390x: smp: Rework cpu start and active tracking

[Janosch Frank <frankja@linux.ibm.com>]

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On 1/20/20 1:06 PM, David Hildenbrand wrote:
> On 17.01.20 11:46, Janosch Frank wrote:
>> The architecture specifies that processing sigp orders may be
>> asynchronous, and this is indeed the case on some hypervisors, so we
>> need to wait until the cpu runs before we return from the setup/start
>> function.
>>
>> As there was a lot of duplicate code, a common function for cpu
>> restarts has been introduced.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>>  lib/s390x/smp.c | 50 ++++++++++++++++++++++++++++---------------------
>>  1 file changed, 29 insertions(+), 21 deletions(-)
>>
>> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
>> index f57f420..84e681d 100644
>> --- a/lib/s390x/smp.c
>> +++ b/lib/s390x/smp.c
>> @@ -104,35 +104,46 @@ int smp_cpu_stop_store_status(uint16_t addr)
>>  	return rc;
>>  }
>>  
>> +static int smp_cpu_restart_nolock(uint16_t addr, struct psw *psw)
>> +{
>> +	int rc;
>> +	struct cpu *cpu = smp_cpu_from_addr(addr);
> 
> I'd exchange these two (reverse christmas tree)

Christmas is over

> 
>> +
>> +	if (!cpu)
>> +		return -1;
> 
> -EINVAL?
> 
>> +	if (psw) {
>> +		cpu->lowcore->restart_new_psw.mask = psw->mask;
>> +		cpu->lowcore->restart_new_psw.addr = psw->addr;
>> +	}
> 
> Does this make sense to have optional? (the other CPU will execute
> random crap if not set, won't it?)

Well, I have restarts in the smp test and I don't want to always pass a
psw if I know what the last restart psw was.
Simply restarting into test_func or wait_for_flag is certainly no problem.

> 
>> +	rc = sigp(addr, SIGP_RESTART, 0, NULL);
>> +	if (rc)
>> +		return rc;
>> +	/*
>> +	 * The order has been accepted, but the actual restart may not
>> +	 * have been performed yet, so wait until the cpu is running.
>> +	 */
>> +	while (!smp_cpu_running(addr))
>> +		mb();
> 
> Should you make sure to stop the CPU before issuing the restart?
> Otherwise you will get false positives if it is still running (but
> hasn't processed the RESTART yet)

Good point


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