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

[Cindy Lu]

On Wed, Mar 27, 2024 at 3:54 PM Jason Wang <jasowang@redhat.com> wrote:
>
> 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.
>
Really sorry for this, vq's vector is 1,2, and will not share with the
configure vector
> > > >
> > > > 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?
>
It will allocate, but  the vector is VIRTIO_NO_VECTOR (0xffff)

then it will called kvm_virtio_pci_vector_use_one()

in this function, there is a check for

    if (vector >= msix_nr_vectors_allocated(dev))

{         return 0;     }

So it will return.

> > 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
>
sure, got it, I have done the Qtest, and it passed
here is the result

Ok:                 794
Expected Fail:      0
Fail:               0
Unexpected Pass:    0
Skipped:            32
Timeout:            0

> > > >
> > > > 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
> > > >
> > >
> >
>