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

[Philippe Mathieu-Daudé]

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;
       }

> +    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;