Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 17 Apr 2020 14:38:38 -0400
Jared Rossi <jrossi@linux.ibm.com> wrote:

> Remove the explicit prefetch check when using vfio-ccw devices.
> This check is not needed as all Linux channel programs are intended
> to use prefetch and will be executed in the same way regardless.

As already commented on the Linux patch: Can we log something, so this
is debuggable if this statement does not hold true in the future?

> 
> Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
> ---
>  hw/vfio/ccw.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> index 50cc2ec75c..e649377b68 100644
> --- a/hw/vfio/ccw.c
> +++ b/hw/vfio/ccw.c
> @@ -74,16 +74,9 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch)
>      struct ccw_io_region *region = vcdev->io_region;
>      int ret;
>  
> -    if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH)) {
> -        if (!(vcdev->force_orb_pfch)) {
> -            warn_once_pfch(vcdev, sch, "requires PFCH flag set");
> -            sch_gen_unit_exception(sch);
> -            css_inject_io_interrupt(sch);
> -            return IOINST_CC_EXPECTED;
> -        } else {
> -            sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH;
> -            warn_once_pfch(vcdev, sch, "PFCH flag forced");
> -        }
> +    if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH) && vcdev->force_orb_pfch) {
> +        sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH;
> +        warn_once_pfch(vcdev, sch, "PFCH flag forced");
>      }

What happens when you run it with an old kernel? I guess the I/O is
only rejected later (after a trip into the kernel), but has that path
ever been tested?

>  
>      QEMU_BUILD_BUG_ON(sizeof(region->orb_area) != sizeof(ORB));