Re: Kernel panic with vhost-vdpa
From: Jason Wang <hidden>
Date: 2021-02-18 08:48:46
Hi Gautam: On 2021/2/15 9:01 下午, Gautam Dawar wrote:
Hi Jason/Michael, I observed a kernel panic while testing vhost-vdpa with Xilinx adapters. Here are the details for your review: Problem statement: When qemu with vhost-vdpa netdevice is run for the first time, it works well. But after the VM is powered off, next qemu run causes kernel panic due to a NULL pointer dereference in irq_bypass_register_producer(). Root cause analysis: 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.
Thanks a lot for reporting this issue.
quoted hunk
Fix details: I think that this issue can be fixed by invoking vhost_vdpa_setup_vq_irq() only when vhost_vdpa_set_status() includes VIRTIO_CONFIG_S_DRIVER_OK in the new status value. This way, there won’t be any stale nodes in the irqbypass module’s producers list which are reset in vhost_vring_call_reset(). Patch:diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index62a9bb0efc55..fdad94e2fbf9 100644--- a/drivers/vhost/vdpa.c +++ b/drivers/vhost/vdpa.c@@ -409,7 +409,6 @@ static long vhost_vdpa_vring_ioctl(structvhost_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: We can also track this issue in Bugzilla ticket 21171 (https://bugzilla.kernel.org/show_bug.cgi?id=211711 <https://bugzilla.kernel.org/show_bug.cgi?id=211711>) and the complete patch is attached with this email.
So vhost supports to remove or switch eventfd through vhost_vdpa_vring_ioctl(). So if userspace want to switch to another eventfd, we should re-do the register and unregister. I think we need to deal this issue in another way. Can we check whether or not the producer is initialized before? Thanks
Regards, Gautam Dawar