Re: [PATCH v4 9/9] s390/vfio_ccw: implement a crw lock

[Eric Farman <farman@linux.ibm.com>]

On 7/25/26 1:03 PM, Matthew Rosato wrote:
> On 7/25/26 11:27 AM, Eric Farman wrote:
>> Unlike the channel_program struct, which covers synchronous I/O
>> submissions and asynchronous interrupts, the CRW region relies
>> exclusively on asynchronous events coming from hardware.
>>
>> Implement a lock to manage the list of those payloads, to ensure
>> they are read cohesively.
>>
>> Fixes: 3f02cb2fd9d2 ("vfio-ccw: Wire up the CRW irq and CRW region")
>> Cc: stable@vger.kernel.org
>> Cc: Farhan Ali <alifm@linux.ibm.com>
>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> 
> ...
> 
>> --- a/drivers/s390/cio/vfio_ccw_private.h
>> +++ b/drivers/s390/cio/vfio_ccw_private.h
>> @@ -98,6 +98,8 @@ struct vfio_ccw_parent {
>>    * @cp: channel program for the current I/O operation
>>    * @irb: irb info received from interrupt
>>    * @scsw: scsw info
>> + * @crw_lock: serialization of CRW information
> 
> I would re-word this to say 'CRW list', to make it a bit more clear that
> the lock does not protect crw_trigger at this time (as discussed in v3).

Yeah, good call.

> 
> With that:
> 
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>

Thanks,

> 
> 
>> + * @crw: list of Channel Report Word elements
>>    * @io_trigger: eventfd ctx for signaling userspace I/O results
>>    * @crw_trigger: eventfd ctx for signaling userspace CRW information
>>    * @req_trigger: eventfd ctx for signaling userspace to return device
>> @@ -122,6 +124,8 @@ struct vfio_ccw_private {
>>   
>>   	struct irb		irb;
>>   	union scsw		scsw;
>> +
>> +	spinlock_t		crw_lock;
>>   	struct list_head	crw;
>>   
>>   	struct eventfd_ctx	*io_trigger;
>