From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55167) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xtv4I-0001FO-5H for qemu-devel@nongnu.org; Thu, 27 Nov 2014 04:08:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xtv4D-0003ho-U1 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 04:08:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49524) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xtv4D-0003hk-N2 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 04:08:49 -0500 Date: Thu, 27 Nov 2014 14:38:42 +0530 From: Amit Shah Message-ID: <20141127090842.GA3899@grmbl.mre> References: <1417067290-20715-1-git-send-email-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417067290-20715-1-git-send-email-david@gibson.dropbear.id.au> Subject: Re: [Qemu-devel] [PATCH] Fix for crash after migration in virtio-rng on bi-endian targets List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: mst@redhat.com, rusty@rustcorp.com.au, agraf@suse.de, qemu-devel@nongnu.org, quintela@redhat.com, pbonzini@redhat.com 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 > --- > 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