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

[Cindy Lu]

On Thu, Mar 28, 2024 at 12:14 PM Jason Wang <jasowang@redhat.com> wrote:
>
> On Wed, Mar 27, 2024 at 5:44 PM Cindy Lu <lulu@redhat.com> wrote:
> >
> > On Wed, Mar 27, 2024 at 5:13 PM Jason Wang <jasowang@redhat.com> wrote:
> > >
> > > On Wed, Mar 27, 2024 at 5:12 PM Jason Wang <jasowang@redhat.com> wrote:
> > > >
> > > > On Wed, Mar 27, 2024 at 4:28 PM Cindy Lu <lulu@redhat.com> wrote:
> > > > >
> > > > > 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.
> > > >
> > > > How about let's just fix this?
> > >
> > > Btw, another question, how does vDPA work here?
> > >
> > > Thanks
> > >
> > the rhel/fedroa guest image will not call  vrtio_stop and virtio_reset
> > during the boot
> > So vector will not change to  VIRTIO_NO_VECTOR. So the vdpa's
> > configure interrupt
> > Should work ok and there is no crash
>
> I mean:
>
> 1) if vDPA can work with the image you used to reproduce the issue
> 2) if current Qemu can work on old kernel without configure interrupt
> support for vDPA
>
Really Sorry for ,  I tried to answer this
1. the vDPA device also can not working in this image,
 Because the irqfd for vector 0 is released. and then guest image
called unmask this vector. These code are all not dependent on vdpa
related processes

2, the current qemu can work with old kernel
because as I debug the old kernel  won't call
msix_fire_vector_notifier for vector 0， and it will not unmask vector
0
Thansk
cindy

> Thanks
>
> > Thanks
> > cindy
> >
> > > >
> > > > Btw, it's better to explain in detail like the above in the next 
> > > > version.
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > > > 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
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