On Wed, 2021-04-21 at 12:01 +0200, Cornelia Huck wrote:
> On Mon, 19 Apr 2021 20:49:06 +0200
> Eric Farman <far...@linux.ibm.com> wrote:
>
> > Commit 690e29b91102 ("vfio-ccw: Refactor ccw irq handler") changed
> > one of the checks for the IRQ notifier registration from saying
> > "the host needs to recognize the only IRQ that exists" to saying
> > "the host needs to recognize ANY IRQ that exists."
> >
> > And this worked fine, because the subsequent change to support the
> > CRW IRQ notifier doesn't get into this code when running on an
> > older
> > kernel, thanks to a guard by a capability region. The later
> > addition
> > of the REQ(uest) IRQ by commit b2f96f9e4f5f ("vfio-ccw: Connect the
> > device request notifier") broke this assumption because there is no
> > matching capability region. Thus, running new QEMU on an older
> > kernel fails with:
> >
> > vfio: unexpected number of irqs 2
> >
> > Let's simply remove the check (and the less-than-helpful message),
> > and make the VFIO_DEVICE_GET_IRQ_INFO ioctl request for the IRQ
> > being processed. If it returns with EINVAL, we can treat it as
> > an unfortunate mismatch but not a fatal error for the guest.
> >
> > Fixes: 690e29b91102 ("vfio-ccw: Refactor ccw irq handler")
> > Fixes: b2f96f9e4f5f ("vfio-ccw: Connect the device request
> > notifier")
> > Signed-off-by: Eric Farman <far...@linux.ibm.com>
> > ---
> > hw/vfio/ccw.c | 15 +++++++--------
> > 1 file changed, 7 insertions(+), 8 deletions(-)
> >
> > diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> > index b2df708e4b..cfbfc3d1a2 100644
> > --- a/hw/vfio/ccw.c
> > +++ b/hw/vfio/ccw.c
> > @@ -411,20 +411,19 @@ static void
> > vfio_ccw_register_irq_notifier(VFIOCCWDevice *vcdev,
> > return;
> > }
> >
> > - if (vdev->num_irqs < irq + 1) {
> > - error_setg(errp, "vfio: unexpected number of irqs %u",
> > - vdev->num_irqs);
>
> Alternative proposal: Change this message to
>
> "vfio: IRQ %u not available (number of irqs %u)"
> and still fail this function, while treating a failure of
> vfio_ccw_register_irq_notifier(vcdev, VFIO_CCW_REQ_IRQ_INDEX, &err);
> in
> vfio_ccw_realize() as a non-fatal error (maybe log a message).
This all sounds fine to me. I'll send a v2 as such.
>
> This allows us to skip doing an ioctl call, of which we already know
> that it would fail.
True, though as this is at the configuration time it's not as critical.
> Still, we can catch cases where a broken kernel e.g.
> provides the crw region, but not the matching irq (I believe
> something
> like that should indeed be a fatal error.)
Well they shouldn't do THAT. :)
>
> > - return;
> > - }
> > -
> > argsz = sizeof(*irq_info);
> > irq_info = g_malloc0(argsz);
> > irq_info->index = irq;
> > irq_info->argsz = argsz;
> > if (ioctl(vdev->fd, VFIO_DEVICE_GET_IRQ_INFO,
> > irq_info) < 0 || irq_info->count < 1) {
> > - error_setg_errno(errp, errno, "vfio: Error getting irq
> > info");
> > - goto out_free_info;
> > + if (errno == EINVAL) {
> > + warn_report("Unable to get information about IRQ %u",
> > irq);
> > + goto out_free_info;
> > + } else {
> > + error_setg_errno(errp, errno, "vfio: Error getting irq
> > info");
> > + goto out_free_info;
> > + }
> > }
> >
> > if (event_notifier_init(notifier, 0)) {
