On Mon, 20 Apr 2020 14:26:17 +0200
Cornelia Huck <coh...@redhat.com> wrote:
> On Fri, 17 Apr 2020 14:38:38 -0400
> Jared Rossi <jro...@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 <jro...@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));
>
Oh, and do we want to deprecate the force prefetch interface in the
future? We probably need to wait a bit, until the kernel changes have
become widely available.
