[PATCH] vhost vdpa: setup vq irq only when set status includes VIRTIO_CONFIG_S_DRIVER_OK

[Gautam Dawar <gdawar.xilinx@xxxxxxxxx>]

When qemu with vhost-vdpa netdevice is run for the first time, it works well.
But after the VM is powered off, the next qemu run causes kernel panic due to a
NULL pointer dereference in irq_bypass_register_producer().

When the VM is powered off, vhost_dev_stop() is invoked which in turn calls
vhost_vdpa_reset_device() causing the irq_bypass producers to be unregistered.

On the next run, when qemu opens the vhost device, the vhost_vdpa_open() file
operation calls vhost_dev_init(). Here, call_ctx->producer memory is cleared
in vhost_vring_call_reset().

Further, when the virtqueues are initialized by vhost_virtqueue_init(),
vhost_vdpa_setup_vq_irq() again registers the irq_bypass producer for each
virtqueue. As the node member of struct irq_bypass_producer is also initialized
to zero, traversal on the producers list causes crash due to NULL pointer
dereference.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711

Signed-off-by: Gautam Dawar <gdawar@xxxxxxxxxx>

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0efc55..fdad94e2fbf9 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -409,7 +409,6 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
                        cb.private = NULL;
                }
                ops->set_vq_cb(vdpa, idx, &cb);
-               vhost_vdpa_setup_vq_irq(v, idx);
                break;

        case VHOST_SET_VRING_NUM:

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