Re: [PATCH v8] virtio-pci: fix use of a released vector

[Cindy Lu]

On Thu, May 9, 2024 at 4:18 AM Michael Tokarev <mjt@tls.msk.ru> wrote:
>
> 15.04.2024 12:34, Michael S. Tsirkin wrote:
> > From: Cindy Lu <lulu@redhat.com>
> >
> > During the booting process of the non-standard image, the behavior of the
> > called function in qemu is as follows:
> >
> > 1. vhost_net_stop() was triggered by guest image. This will call the 
> > function
> > virtio_pci_set_guest_notifiers() with assgin= false,
> > virtio_pci_set_guest_notifiers(） will release the irqfd for vector 0
> >
> > 2. virtio_reset() was triggered, this will set configure vector to 
> > VIRTIO_NO_VECTOR
> >
> > 3.vhost_net_start() was called (at this time, the configure vector is
> > still VIRTIO_NO_VECTOR) and then call virtio_pci_set_guest_notifiers() with
> > assgin=true, so the irqfd for vector 0 is still not "init" during this 
> > process
> >
> > 4. The system continues to boot and sets the vector back to 0. After that
> > msix_fire_vector_notifier() was triggered to unmask the vector 0 and  meet 
> > the crash
> >
> > To fix the issue, we need to support changing the vector after 
> > VIRTIO_CONFIG_S_DRIVER_OK is set.
>
> This change breaks both 9.0 and stable-8.2.3:
>
> https://gitlab.com/qemu-project/qemu/-/issues/2321
> https://gitlab.com/qemu-project/qemu/-/issues/2334
>
> So something's not right here.
>
> Thanks,
>
I have checked the stack, seems there is a  crash while set the vector
to NO_VECTOER?

#0  kvm_virtio_pci_vq_vector_release (proxy=0x55bd979fd130,
vector=<optimized out>) at ../hw/virtio/virtio-pci.c:834
#1  kvm_virtio_pci_vector_release_one
(proxy=proxy@entry=0x55bd979fd130, queue_no=queue_no@entry=0) at
../hw/virtio/virtio-pci.c:965
#2  0x000055bd9380c430 in virtio_pci_set_vector (vdev=0x55bd97a05500,
proxy=0x55bd979fd130, queue_no=0, old_vector=1, new_vector=65535)
    at ../hw/virtio/virtio-pci.c:1445
#3  0x000055bd939c5490 in memory_region_write_accessor
(mr=0x55bd979fdc70, addr=26, value=<optimized out>, size=2,
shift=<optimized out>,
    mask=<optimized out>, attrs=...) at ../system/memory.c:497

I will try to reproduce and work in it

thanks
Cindy


> /mjt
>
> ...
> > MST: coding style and typo fixups
> >
> > Fixes: f9a09ca3ea ("vhost: add support for configure interrupt")
> > Cc: qemu-stable@nongnu.org
> > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > Message-Id: <20240412062750.475180-1-lulu@redhat.com>
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >   hw/virtio/virtio-pci.c | 37 +++++++++++++++++++++++++++++++++++--
> >   1 file changed, 35 insertions(+), 2 deletions(-)
> >
> > v7->v8:
> > more cleanups, suggested by Philip
> >
> > still untested, i just got involved to help address coding style
> > issues
> >
> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index cb6940fc0e..cb159fd078 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1424,6 +1424,38 @@ static int virtio_pci_add_mem_cap(VirtIOPCIProxy 
> > *proxy,
> >       return offset;
> >   }
> >
> > +static void virtio_pci_set_vector(VirtIODevice *vdev,
> > +                                  VirtIOPCIProxy *proxy,
> > +                                  int queue_no, uint16_t old_vector,
> > +                                  uint16_t new_vector)
> > +{
> > +    bool kvm_irqfd = (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
> > +        msix_enabled(&proxy->pci_dev) && kvm_msi_via_irqfd_enabled();
> > +
> > +    if (new_vector == old_vector) {
> > +        return;
> > +    }
> > +
> > +    /*
> > +     * If the device uses irqfd and the vector changes after DRIVER_OK is
> > +     * set, we need to release the old vector and set up the new one.
> > +     * Otherwise just need to set the new vector on the device.
> > +     */
> > +    if (kvm_irqfd && old_vector != VIRTIO_NO_VECTOR) {
> > +        kvm_virtio_pci_vector_release_one(proxy, queue_no);
> > +    }
> > +    /* Set the new vector on the device. */
> > +    if (queue_no == VIRTIO_CONFIG_IRQ_IDX) {
> > +        vdev->config_vector = new_vector;
> > +    } else {
> > +        virtio_queue_set_vector(vdev, queue_no, new_vector);
> > +    }
> > +    /* If the new vector changed need to set it up. */
> > +    if (kvm_irqfd && new_vector != VIRTIO_NO_VECTOR) {
> > +        kvm_virtio_pci_vector_use_one(proxy, queue_no);
> > +    }
> > +}
> > +
> >   int virtio_pci_add_shm_cap(VirtIOPCIProxy *proxy,
> >                              uint8_t bar, uint64_t offset, uint64_t length,
> >                              uint8_t id)
> > @@ -1570,7 +1602,8 @@ static void virtio_pci_common_write(void *opaque, 
> > hwaddr addr,
> >           } else {
> >               val = VIRTIO_NO_VECTOR;
> >           }
> > -        vdev->config_vector = val;
> > +        virtio_pci_set_vector(vdev, proxy, VIRTIO_CONFIG_IRQ_IDX,
> > +                              vdev->config_vector, val);
> >           break;
> >       case VIRTIO_PCI_COMMON_STATUS:
> >           if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) {
> > @@ -1610,7 +1643,7 @@ static void virtio_pci_common_write(void *opaque, 
> > hwaddr addr,
> >           } else {
> >               val = VIRTIO_NO_VECTOR;
> >           }
> > -        virtio_queue_set_vector(vdev, vdev->queue_sel, val);
> > +        virtio_pci_set_vector(vdev, proxy, vdev->queue_sel, vector, val);
> >           break;
> >       case VIRTIO_PCI_COMMON_Q_ENABLE:
> >           if (val == 1) {
>
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