Re: [kvm-unit-tests 2/2] s390x/smp: add minimal test for sigp sense running status

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 30.03.20 12:58, David Hildenbrand wrote:
> On 30.03.20 10:49, Christian Borntraeger wrote:
>> make sure that sigp sense running status returns a sane value for
>> stopped CPUs.
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>>  lib/s390x/smp.c |  2 +-
>>  lib/s390x/smp.h |  2 +-
>>  s390x/smp.c     | 11 +++++++++++
>>  3 files changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
>> index 5ed8b7b..492cb05 100644
>> --- a/lib/s390x/smp.c
>> +++ b/lib/s390x/smp.c
>> @@ -58,7 +58,7 @@ bool smp_cpu_stopped(uint16_t addr)
>>  	return !!(status & (SIGP_STATUS_CHECK_STOP|SIGP_STATUS_STOPPED));
>>  }
>>  
>> -bool smp_cpu_running(uint16_t addr)
>> +bool smp_sense_running_status(uint16_t addr)
>>  {
>>  	if (sigp(addr, SIGP_SENSE_RUNNING, 0, NULL) != SIGP_CC_STATUS_STORED)
>>  		return true;
>> diff --git a/lib/s390x/smp.h b/lib/s390x/smp.h
>> index a8b98c0..639ec92 100644
>> --- a/lib/s390x/smp.h
>> +++ b/lib/s390x/smp.h
>> @@ -40,7 +40,7 @@ struct cpu_status {
>>  int smp_query_num_cpus(void);
>>  struct cpu *smp_cpu_from_addr(uint16_t addr);
>>  bool smp_cpu_stopped(uint16_t addr);
>> -bool smp_cpu_running(uint16_t addr);
>> +bool smp_sense_running_status(uint16_t addr);
>>  int smp_cpu_restart(uint16_t addr);
>>  int smp_cpu_start(uint16_t addr, struct psw psw);
>>  int smp_cpu_stop(uint16_t addr);
>> diff --git a/s390x/smp.c b/s390x/smp.c
>> index 79cdc1f..f9f143d 100644
>> --- a/s390x/smp.c
>> +++ b/s390x/smp.c
>> @@ -210,6 +210,16 @@ static void test_emcall(void)
>>  	report_prefix_pop();
>>  }
>>  
>> +static void test_sense_running(void)
>> +{
>> +	report_prefix_push("sense_running");
>> +	/* make sure CPU is stopped */
>> +	smp_cpu_stop(1);
>> +	report(!smp_sense_running_status(1), "CPU1 sense claims not running");
>> +	report_prefix_pop();
>> +}
>> +
>> +
>>  /* Used to dirty registers of cpu #1 before it is reset */
>>  static void test_func_initial(void)
>>  {
>> @@ -319,6 +329,7 @@ int main(void)
>>  	test_store_status();
>>  	test_ecall();
>>  	test_emcall();
>> +	test_sense_running();
>>  	test_reset();
>>  	test_reset_initial();
>>  	smp_cpu_destroy(1);
>>
> 
> In kvm, we set/clear via kvm_arch_vcpu_load/kvm_arch_vcpu_put. This
> means, that a VCPU will also be indicated as running, in case we perform
> certain VCPU IOCTLs, while the VCPU is already stopped.
> 
> Especially, there is a theoretical race between stopping a VCPU, and it
> still being in the kernel, and the other thread sensing the running
> status. This is the case with !kvm_s390_user_cpu_state_ctrl(), when
> leaving handle_stop() but also with kvm_s390_user_cpu_state_ctrl(), when
> setting the MP state via kvm_arch_vcpu_ioctl_set_mpstate().

I think I will just busy wait until the target is not running. This must happen and a timeout indicates a failure.