Re: [PATCH] vfio: ccw: only free cp on final interrupt

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

On 03/11/2019 06:20 AM, Cornelia Huck wrote:
> When we get an interrupt for a channel program, it is not
> necessarily the final interrupt; for example, the issuing
> guest may request an intermediate interrupt by specifying
> the program-controlled-interrupt flag on a ccw.
> 
> We must not switch the state to idle if the interrupt is not
> yet final; even more importantly, we must not free the translated
> channel program if the interrupt is not yet final, or the host
> can crash during cp rewind.
> 
> Fixes: e5f84dbaea59 ("vfio: ccw: return I/O results asynchronously")
> Cc: stable@vger.kernel.org # v4.12+
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>

Reviewed-by: Eric Farman <farman@linux.ibm.com>

> ---
> 
> Previously part of "vfio-ccw: rework ssch state handling". Please review,
> I plan to send a pull req asap.
> 
> ---
>   drivers/s390/cio/vfio_ccw_drv.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
> index a10cec0e86eb..0b3b9de45c60 100644
> --- a/drivers/s390/cio/vfio_ccw_drv.c
> +++ b/drivers/s390/cio/vfio_ccw_drv.c
> @@ -72,20 +72,24 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
>   {
>   	struct vfio_ccw_private *private;
>   	struct irb *irb;
> +	bool is_final;
>   
>   	private = container_of(work, struct vfio_ccw_private, io_work);
>   	irb = &private->irb;
>   
> +	is_final = !(scsw_actl(&irb->scsw) &
> +		     (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
>   	if (scsw_is_solicited(&irb->scsw)) {
>   		cp_update_scsw(&private->cp, &irb->scsw);
> -		cp_free(&private->cp);
> +		if (is_final)
> +			cp_free(&private->cp);
>   	}
>   	memcpy(private->io_region->irb_area, irb, sizeof(*irb));
>   
>   	if (private->io_trigger)
>   		eventfd_signal(private->io_trigger, 1);
>   
> -	if (private->mdev)
> +	if (private->mdev && is_final)
>   		private->state = VFIO_CCW_STATE_IDLE;
>   }
>   
>