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

David Hildenbrand
2021-12-15T13:24:36Z

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.

--
Thanks,

David / dhildenb