Virtualization - Feb 2021 - [PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

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_vdpa_clean_irq() misses on calling
irq_bypass_unregister_producer() for irq 0 because of the existing check.

This leaves stale producer nodes, which are reset in
vhost_vring_call_reset()
when vhost_dev_init() is invoked during the second qemu run.

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 at xilinx.com>


diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0efc55..d1c3a33c6239 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)

        for (i = 0; i < v->nvqs; i++) {
                vq = &v->vqs[i];
-               if (vq->call_ctx.producer.irq)
+               if (vq->call_ctx.producer.irq >= 0)

irq_bypass_unregister_producer(&vq->call_ctx.producer);
        }
 }
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On 2021/2/22 ??5:13, Gautam Dawar wrote:
> 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_vdpa_clean_irq() misses on calling
> irq_bypass_unregister_producer() for irq 0 because of the existing check.
>
> This leaves stale producer nodes, which are reset in 
> vhost_vring_call_reset()
> when vhost_dev_init() is invoked during the second qemu run.
>
> 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 at xilinx.com <mailto:gdawar at
xilinx.com>>
>
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 62a9bb0efc55..d1c3a33c6239 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)
>
> ? ? ? ? for (i = 0; i < v->nvqs; i++) {
> ? ? ? ? ? ? ? ? vq = &v->vqs[i];
> - ? ? ? ? ? ? ? if (vq->call_ctx.producer.irq)
> + ? ? ? ? ? ? ? if (vq->call_ctx.producer.irq >= 0)
> irq_bypass_unregister_producer(&vq->call_ctx.producer);

Since it's impossible to have an irq < 0 ( see 
vhost_vdap_setup_vq_irq()), I think we can simply remove the check above.

Then we can call vhost_vdpa_unsetup_vq_irq() here to avoid temporary 
variable like vq.

Thanks

> ? ? ? ? }
> ?}