On Thu, 15 Dec 2011 10:27:50 +0200, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> On Tue, Dec 13, 2011 at 12:51:20PM +1030, Rusty Russell wrote:
> I mean like this in block:
>
>
>
> /* Host must always specify the capacity. */
> vdev->config->get(vdev, offsetof(struct virtio_blk_config,
> capacity),
> &capacity, sizeof(capacity));
>
> /* If capacity is too big, truncate with warning. */
> if ((sector_t)capacity != capacity) {
> dev_warn(&vdev->dev, "Capacity %llu too large:
> truncating\n",
> (unsigned long long)capacity);
> capacity = (sector_t)-1;
> }
>
>
> Now let's assume capacity field is changed from 0x8000 to 0x10000
> on host. Is it possible that we read two upper bytes
> before the change so we see 0x0000....
> and 2 lower bytes after the change
> so we see 0x....0000 and resulting capacity appears
> to be 0?
>
> If no why not?
Same issue in reverse with the guest setting the MAC address in
virtio_net, if the host were reading it. And virtio_balloon? We have
ignored it, so far.
Perhaps a new feature VIRTIO_F_UNSTABLE? Which (unlike other features)
appears and vanishes around config writes by either side? Kind of a
hack though...
Cheers,
Rusty.
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