Re: [RFC PATCH v5 1/1] KVM: s390: Clarify SIGP orders versus STOP/RESTART

David Hildenbrand
2021-12-15T14:02:31Z

On 15.12.21 14:57, Christian Borntraeger wrote:
>
>
> Am 15.12.21 um 14:24 schrieb David Hildenbrand:
>> On 13.12.21 22:05, Eric Farman wrote:
>>> With KVM_CAP_S390_USER_SIGP, there are only five Signal Processor
>>> orders (CONDITIONAL EMERGENCY SIGNAL, EMERGENCY SIGNAL, EXTERNAL CALL,
>>> SENSE, and SENSE RUNNING STATUS) which are intended for frequent use
>>> and thus are processed in-kernel. The remainder are sent to userspace
>>> with the KVM_CAP_S390_USER_SIGP capability. Of those, three orders
>>> (RESTART, STOP, and STOP AND STORE STATUS) have the potential to
>>> inject work back into the kernel, and thus are asynchronous.
>>>
>>> Let's look for those pending IRQs when processing one of the in-kernel
>>> SIGP orders, and return BUSY (CC2) if one is in process. This is in
>>> agreement with the Principles of Operation, which states that only one
>>> order can be "active" on a CPU at a time.
>>>
>>> Suggested-by: David Hildenbrand <david@redhat.com>
>>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>>> ---
>>
>> In general, LGTM. As raised, with SIGP RESTART there are other cases we
>> could fix in the kernel, but they are of very low priority IMHO.
>
> Does that qualify as an RB, assuming that we can fix the other cases later on?
>

Certainly an Acked-by: David Hildenbrand <david@redhat.com> , to fully
review I need some more time (maybe tomorrow)

--
Thanks,

David / dhildenb