Re: [PATCH v7] virtio-pci: Fix the crash that the vector was used after released.

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 15, 2024 at 11:23:46AM +0200, Philippe Mathieu-Daudé wrote:
> On 15/4/24 11:19, 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.
> 
> 
> > 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>
> > ---
> > 
> > To expedite fixed lots of style issues myself.
> > Completely untested - guys can you pls test and ack?
> > 
> > 
> >   hw/virtio/virtio-pci.c | 41 +++++++++++++++++++++++++++++++++++++++--
> >   1 file changed, 39 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index cb6940fc0e..e9edd57339 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1424,6 +1424,34 @@ static int virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,
> >       return offset;
> >   }
> > +static void virtio_pci_set_and_change_vector(VirtIODevice *vdev,
> > +                                             VirtIOPCIProxy *proxy,
> > +                                             int queue_no, uint16_t old_vector,
> > +                                             uint16_t new_vector)
> > +{
> 
> Alternatively:
> 
>        if (new_vector == old_vector) {
>            return;
>        }


True. And in fact callers do not need check this.
Let me do v8.


> > +    bool kvm_irqfd = (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
> > +        msix_enabled(&proxy->pci_dev) && kvm_msi_via_irqfd_enabled();
> > +
> > +    /*
> > +     * 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 +1598,12 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
> >           } else {
> >               val = VIRTIO_NO_VECTOR;
> >           }
> > -        vdev->config_vector = val;
> > +        vector = vdev->config_vector;
> > +        /* Check if we need to change the vector. */
> > +        if (val != vector) {
> > +            virtio_pci_set_and_change_vector(vdev, proxy, VIRTIO_CONFIG_IRQ_IDX,
> > +                                             vector, val);
> > +        }
> >           break;