Re: [RFC 0/2] disable the configuration interrupt for the unsupported device

[Jason Wang]

On Wed, Mar 27, 2024 at 2:03 PM Cindy Lu <lulu@redhat.com> wrote:
>
> On Wed, Mar 27, 2024 at 11:05 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > Hi Cindy:
> >
> > On Wed, Mar 27, 2024 at 9:29 AM Cindy Lu <lulu@redhat.com> wrote:
> > >
> > > we need a crash in Non-standard image, here is the jira for this 
> > > https://issues.redhat.com/browse/RHEL-28522
> > > The root cause of the issue is that an IRQFD was used without 
> > > initialization..
> > >
> > > During the booting process of the Vyatta image, the behavior of the 
> > > called function in qemu is as follows:
> > >
> > > 1. vhost_net_stop() was called, this will call the function
> > > virtio_pci_set_guest_notifiers() with assgin= false, and
> > > virtio_pci_set_guest_notifiers(） will release the irqfd for vector 0
> >
> > Before vhost_net_stop(), do we know which vector is used by which queue?
> >
> before this stop, vdev->config_verctor is get from
> virtio_pci_common_read/virtio_pci_common_write
> it was set to vector 0

I basically meant if vector 0 is shared with some virtqueues here.

> > >
> > > 2. virtio_reset() was called -->set configure vector to VIRTIO_NO_VECTORt
> > >
> > > 3.vhost_net_start() was called (at this time the configure vector is
> > > still VIRTIO_NO_VECTOR) and call virtio_pci_set_guest_notifiers() with
> > > assgin= true, so the irqfd for vector 0 was not "init" during this process
> >
> > How does the configure vector differ from the virtqueue vector here?
> >
> All the vectors are VIRTIO_NO_VECTOR (including vq). any
> msix_fire_vector_notifier()
> been called will cause the crash at this time.

Won't virtio_pci_set_guest_notifiers() will try to allocate irqfd when
the assignment is true?

> So I think this should
> be a bug in this guest image

The point is Qemu should not crash even if the guest driver is buggy.

It would be nice if we can have a qtest for this on top.

Thanks

> > >
> > > 4. The system continues to boot and msix_fire_vector_notifier() was
> > > called unmask the vector 0 and then met the crash
> > > [msix_fire_vector_notifier] 112 called vector 0 is_masked 1
> > > [msix_fire_vector_notifier] 112 called vector 0 is_masked 0
> > >
> > > The reason for not reproducing in RHEL/fedora guest image is because
> > > REHL/Fedora doesn't have the behavior of calling vhost_net_stop and then 
> > > virtio_reset, and also won't call msix_fire_vector_notifier for vector 0 
> > > during system boot.
> > >
> > > The reason for not reproducing before configure interrupt support is 
> > > because
> > > vector 0 is for configure interrupt,  before the support for configure 
> > > interrupts, the notifier process will not handle vector 0.
> > >
> > > For the device Vyatta using, it doesn't support configure interrupts at 
> > > all, So we plan to disable the configure interrupts in unsupported device
> >
> > Btw, let's tweak the changelog, it's a little bit hard to understand.
> >
> sure will do
> thanks
> Cindy
> > Thanks
> >
> > >
> > > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > >
> > > Cindy Lu (2):
> > >   virtio-net: disable the configure interrupt for not support device
> > >   virtio-pci: check if the configure interrupt enable
> > >
> > >  hw/net/virtio-net.c        |  5 ++++-
> > >  hw/virtio/virtio-pci.c     | 41 +++++++++++++++++++++-----------------
> > >  hw/virtio/virtio.c         |  1 +
> > >  include/hw/virtio/virtio.h |  1 +
> > >  4 files changed, 29 insertions(+), 19 deletions(-)
> > >
> > > --
> > > 2.43.0
> > >
> >
>