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

[Peter Maydell]

On 27 November 2014 at 09:26, Markus Armbruster <address@hidden> wrote:
> 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 :)

So do you want this patch in 2.2? I was planning to put in the
virtio-vs-xen fixes today and tag rc4, so it's not too late if you're
confident this patch is good. Let me know if you think it should go in,
and I can apply it to master directly.

-- PMM