Re: [Qemu-devel] [PATCH] Fix for crash after migration in virtio-rng on bi-endian targets

[Markus Armbruster]

David Gibson <address@hidden> writes:

> VirtIO devices now remember which endianness they're operating in in order
> to support targets which may have guests of either endianness, such as
> powerpc.  This endianness state is transferred in a subsection of the
> virtio device's information.
>
> With virtio-rng this can lead to an abort after a loadvm hitting the
> assert() in virtio_is_big_endian().  This can be reproduced by doing a
> migrate and load from file on a bi-endian target with a virtio-rng device.
> The actual guest state isn't particularly important to triggering this.
>
> The cause is that virtio_rng_load_device() calls virtio_rng_process() which
> accesses the ring and thus needs the endianness.  However,
> virtio_rng_process() is called via virtio_load() before it loads the
> subsections.  Essentially the ->load callback in VirtioDeviceClass should
> only be used for actually reading the device state from the stream, not for
> post-load re-initialization.
>
> This patch fixes the bug by moving the virtio_rng_process() after the call
> to virtio_load().  Better yet would be to convert virtio to use vmsd and
> have the virtio_rng_process() as a post_load callback, but that's a bigger
> project for another day.
>
> This is bugfix, and should be considered for the 2.2 branch.

"[PATCH for-2.2]" would have been a good idea then.  Next time :)