linux-kernel - Re: [PATCH 1/2] virtio: Reduce BUG if total

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Date:   Fri, 11 Aug 2017 00:41:47 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "Richard W.M. Jones" <rjones@...hat.com>
Cc:     jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com,
        jasowang@...hat.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, hch@....de,
        pbonzini@...hat.com
Subject: Re: [PATCH 1/2] virtio: Reduce BUG if total_sg > virtqueue size to
 WARN.

On Thu, Aug 10, 2017 at 10:35:11PM +0100, Richard W.M. Jones wrote:
> On Fri, Aug 11, 2017 at 12:31:44AM +0300, Michael S. Tsirkin wrote:
> > Then we probably should fail probe if vq size is too small.
> 
> What does this mean?
> 
> Rich.

We must prevent driver from submitting s/g lists > vq size to device.


Either tell linux to avoid s/g lists that are too long, or
simply fail request if this happens, or refuse to attach driver to device.

Later option would look something like this within probe:

        for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++)
		if (vqs[i]->num < MAX_SG_USED_BY_LINUX)
			goto err;


I don't know what's MAX_SG_USED_BY_LINUX though.

> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
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