Re: [kvm-unit-tests PATCH v11 8/9] s390x: css: msch, enable test

Pierre Morel
2020-07-09T13:58:14Z

On 2020-07-09 15:52, Cornelia Huck wrote:
> On Thu, 9 Jul 2020 15:41:56 +0200
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> On 2020-07-09 15:30, Cornelia Huck wrote:
>>> On Thu, 9 Jul 2020 15:12:05 +0200
>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>
>>>> On 2020-07-09 13:40, Cornelia Huck wrote:
>>>>> On Thu, 9 Jul 2020 10:07:47 +0200
>>>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>>>
>>>>>> A second step when testing the channel subsystem is to prepare a channel
>>>>>> for use.
>>>>>> This includes:
>>>>>> - Get the current subchannel Information Block (SCHIB) using STSCH
>>>>>> - Update it in memory to set the ENABLE bit and the specified ISC
>>>>>> - Tell the CSS that the SCHIB has been modified using MSCH
>>>>>> - Get the SCHIB from the CSS again to verify that the subchannel is
>>>>>> enabled and uses the specified ISC.
>>>>>> - If the command succeeds but subchannel is not enabled or the ISC
>>>>>> field is not as expected, retry a predefined retries count.
>>>>>> - If the command fails, report the failure and do not retry, even
>>>>>> if cc indicates a busy/status pending as we do not expect this.
>>>>>>
>>>>>> This tests the MSCH instruction to enable a channel successfully.
>>>>>> Retries are done and in case of error, and if the retries count
>>>>>> is exceeded, a report is made.
>>>>>>
>>>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>>>>> Acked-by: Thomas Huth <thuth@redhat.com>
>>>>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>>>>> ---
>>>>>> lib/s390x/css.h | 8 +++--
>>>>>> lib/s390x/css_lib.c | 72 +++++++++++++++++++++++++++++++++++++++++++++
>>>>>> s390x/css.c | 15 ++++++++++
>>>>>> 3 files changed, 92 insertions(+), 3 deletions(-)
>>>>>
>>>>> (...)
>>>>>
>>>>>> +/*
>>>>>> + * css_msch: enable subchannel and set with specified ISC
>>>>>
>>>>> "css_enable: enable the subchannel with the specified ISC"
>>>>>
>>>>> ?
>>>>>
>>>>>> + * @schid: Subchannel Identifier
>>>>>> + * @isc : number of the interruption subclass to use
>>>>>> + * Return value:
>>>>>> + * On success: 0
>>>>>> + * On error the CC of the faulty instruction
>>>>>> + * or -1 if the retry count is exceeded.
>>>>>> + */
>>>>>> +int css_enable(int schid, int isc)
>>>>>> +{
>>>>>> + struct pmcw *pmcw = &schib.pmcw;
>>>>>> + int retry_count = 0;
>>>>>> + uint16_t flags;
>>>>>> + int cc;
>>>>>> +
>>>>>> + /* Read the SCHIB for this subchannel */
>>>>>> + cc = stsch(schid, &schib);
>>>>>> + if (cc) {
>>>>>> + report_info("stsch: sch %08x failed with cc=%d", schid, cc);
>>>>>> + return cc;
>>>>>> + }
>>>>>> +
>>>>>> + flags = PMCW_ENABLE | (isc << PMCW_ISC_SHIFT);
>>>>>> + if ((pmcw->flags & flags) == flags) {
>>>>>
>>>>> I think you want (pmcw->flags & PMCW_ENABLE) == PMCW_ENABLE -- this
>>>>> catches the case of "subchannel has been enabled before, but with a
>>>>> different isc".
>>>>
>>>> If with a different ISC, we need to modify the ISC.
>>>> Don't we ?
>>>
>>> I think that's a policy decision (I would probably fail and require a
>>> disable before setting another isc, but that's a matter of taste).
>>>
>>> Regardless, I think the current check doesn't even catch the 'different
>>> isc' case?
>>
>> hum, right.
>> If it is OK I remove this one.
>> And I must rework the same test I do later
>> in this patch.
>
> So, you mean checking for PMCW_ENABLE? Or not at all?
>
> (I'd check for PMCW_ENABLE.)
>

- if ((pmcw->flags & flags) == flags) {
+ if ((pmcw->flags & (PMCW_ISC_MASK | PMCW_ENABLE)) == flags) {
report_info("stsch: sch %08x already enabled", schid);
return 0;
}

I keep both, otherwise I return 0 without setting the ISC.
then I have another error:

retry:
/* Update the SCHIB to enable the channel and set the ISC */
+ pmcw->flags &= ~(PMCW_ISC_MASK | PMCW_ENABLE);
pmcw->flags |= flags;

and finaly the same as the first later...

- if ((pmcw->flags & flags) == flags) {
+ if ((pmcw->flags & (PMCW_ISC_MASK | PMCW_ENABLE)) == flags) {
report_info("stsch: sch %08x successfully modified
after %d retries",
schid, retry_count);

is better I think.
What do you think?

--
Pierre Morel
IBM Lab Boeblingen