Re: [kvm-unit-tests PATCH v4 4/9] s390x: smp: Rework cpu start and active tracking

Janosch Frank
2020-01-22T08:25:33Z

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On 1/21/20 6:40 PM, David Hildenbrand wrote:
> On 21.01.20 14:42, 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);
>> +
>> + if (!cpu)
>> + return -1;
>> + if (psw) {
>> + cpu->lowcore->restart_new_psw.mask = psw->mask;
>> + cpu->lowcore->restart_new_psw.addr = psw->addr;
>> + }
>> + 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();
>> + cpu->active = true;
>> + return 0;
>> +}
>> +
>
> Just wondering what happened to my comment

It probably got lost in your other change requests :)

>
> "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)"
>
> ?
>
> IOW, should we have a SIGP_STOP before issuing the SIGP_RESTART?

Yes, that would be cleaner.

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