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Re: [Qemu-devel] [PATCH] Fix for crash after migration in virtio-rng on
From: |
Amit Shah |
Subject: |
Re: [Qemu-devel] [PATCH] Fix for crash after migration in virtio-rng on bi-endian targets |
Date: |
Thu, 27 Nov 2014 14:38:42 +0530 |
On (Thu) 27 Nov 2014 [16:48:10], David Gibson wrote:
> 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.
Agreed.
> 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.
This is undoing most of 3902d49e13c2428bd6381cfdf183103ca4477c1f ,
added Greg to CC list.
Did you try this on x86 guests, or with multiple rng devices?
(keeping context for Greg)
> Signed-off-by: David Gibson <address@hidden>
> ---
> hw/virtio/virtio-rng.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
> index e85a979..473c044 100644
> --- a/hw/virtio/virtio-rng.c
> +++ b/hw/virtio/virtio-rng.c
> @@ -113,20 +113,22 @@ static void virtio_rng_save(QEMUFile *f, void *opaque)
>
> static int virtio_rng_load(QEMUFile *f, void *opaque, int version_id)
> {
> + VirtIORNG *vrng = opaque;
> + int ret;
> +
> if (version_id != 1) {
> return -EINVAL;
> }
> - return virtio_load(VIRTIO_DEVICE(opaque), f, version_id);
> -}
> + ret = virtio_load(VIRTIO_DEVICE(vrng), f, version_id);
> + if (ret != 0) {
> + return ret;
> + }
>
> -static int virtio_rng_load_device(VirtIODevice *vdev, QEMUFile *f,
> - int version_id)
> -{
> /* We may have an element ready but couldn't process it due to a quota
> * limit. Make sure to try again after live migration when the quota may
> * have been reset.
> */
> - virtio_rng_process(VIRTIO_RNG(vdev));
> + virtio_rng_process(vrng);
>
> return 0;
> }
> @@ -231,7 +233,6 @@ static void virtio_rng_class_init(ObjectClass *klass,
> void *data)
> vdc->realize = virtio_rng_device_realize;
> vdc->unrealize = virtio_rng_device_unrealize;
> vdc->get_features = get_features;
> - vdc->load = virtio_rng_load_device;
> }
>
> static void virtio_rng_initfn(Object *obj)
Thanks,
Amit