From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37161) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fY9Ck-0003XQ-VS for qemu-devel@nongnu.org; Wed, 27 Jun 2018 08:05:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fY9Cg-0005ni-SW for qemu-devel@nongnu.org; Wed, 27 Jun 2018 08:05:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50198) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fY9Cg-0005n8-K7 for qemu-devel@nongnu.org; Wed, 27 Jun 2018 08:05:42 -0400 Date: Wed, 27 Jun 2018 08:05:41 -0400 (EDT) From: Pankaj Gupta Message-ID: <410633343.46328776.1530101141460.JavaMail.zimbra@redhat.com> In-Reply-To: <20180627112741.GH30628@redhat.com> References: <20180627112520.26085-1-pagupta@redhat.com> <20180627112741.GH30628@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2] virtio-rng: process pending requests when driver is ready List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Daniel =?utf-8?Q?P=2E_Berrang=C3=A9?= Cc: amit@kernel.org, stefanha@redhat.com, qemu-devel@nongnu.org, slopezpa@redhat.com, mst@redhat.com > > On Wed, Jun 27, 2018 at 04:55:20PM +0530, Pankaj Gupta wrote: > > virtio-rng device causing old guest kernels(2.6.32) to hang on latest > > qemu. > > The driver attempts to read from the virtio-rng device too early in it's > > initialization. Qemu detects guest is not ready and returns, resulting in > > hang. > > Presumably this all worked previously at some point, so do you know what > change in QEMU has caused a regression in this regard. Latest qemu(2.x) has this issue with older guest kernel(2.6.32) versions. But it does work properly with upstream guest kernel because the way virtio-rng driver is reworked, it sends request to virtio-rng driver when(before) there is read call. If guest driver is ready when it notifies qemu this works fine. There are number of changes in guest virtio/driver code infrastructure as well as qemu side, I don't know exact commit after which this stopped working for older guest kernels. Thanks, Pankaj > > > > > Fix is to handle pending request when guest is running and driver status > > is > > set to 'VIRTIO_CONFIG_S_DRIVER_OK'. > > > > Reported-by: Sergio lopez > > Signed-off-by: Stefan Hajnoczi > > Signed-off-by: Pankaj Gupta > > --- > > v1->v2: Update new status value early only for virtio-rng (Stefan) > > > > hw/virtio/virtio-rng.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c > > index 289bbcac03..855f1b41d1 100644 > > --- a/hw/virtio/virtio-rng.c > > +++ b/hw/virtio/virtio-rng.c > > @@ -156,6 +156,19 @@ static void check_rate_limit(void *opaque) > > vrng->activate_timer = true; > > } > > > > +static void virtio_rng_set_status(VirtIODevice *vdev, uint8_t status) > > +{ > > + VirtIORNG *vrng = VIRTIO_RNG(vdev); > > + > > + if (!vdev->vm_running) { > > + return; > > + } > > + vdev->status = status; > > + > > + /* Something changed, try to process buffers */ > > + virtio_rng_process(vrng); > > +} > > + > > static void virtio_rng_device_realize(DeviceState *dev, Error **errp) > > { > > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > > @@ -261,6 +274,7 @@ 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->set_status = virtio_rng_set_status; > > } > > > > static const TypeInfo virtio_rng_info = { > > -- > > 2.14.3 > > > > > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange > |:| > |: https://libvirt.org -o- https://fstop138.berrange.com > |:| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange > |:| > >