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

[Matthew Rosato <mjrosato@linux.ibm.com>]

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).

With that:

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


> + * @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;