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Tsirkin" To: Jason Wang Subject: Re: [BUG] vhost-vdpa: qemu-system-s390x crashes with second virtio-net-ccw device Message-ID: <20200727074221-mutt-send-email-mst@kernel.org> References: <20200724152718.4e1cbc9e.cohuck@redhat.com> <20200724092906-mutt-send-email-mst@kernel.org> <20200724165627.70c6dfd6.cohuck@redhat.com> <20200724111512-mutt-send-email-mst@kernel.org> <20200724173448.18773aec.cohuck@redhat.com> <5a0dfa0b-5a1d-e7d2-1785-8cca6ddb9db8@redhat.com> <20200727084310.7d29ec6d.cohuck@redhat.com> <676ce079-adf6-a279-c2ea-68f43146e2ac@redhat.com> <20200727104148.4ae49715.cohuck@redhat.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 00:16:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, Cornelia Huck , qemu-devel@nongnu.org, Cindy Lu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 27, 2020 at 04:51:23PM +0800, Jason Wang wrote: > > On 2020/7/27 下午4:41, Cornelia Huck wrote: > > On Mon, 27 Jul 2020 15:38:12 +0800 > > Jason Wang wrote: > > > > > On 2020/7/27 下午2:43, Cornelia Huck wrote: > > > > On Sat, 25 Jul 2020 08:40:07 +0800 > > > > Jason Wang wrote: > > > > > On 2020/7/24 下午11:34, Cornelia Huck wrote: > > > > > > On Fri, 24 Jul 2020 11:17:57 -0400 > > > > > > "Michael S. Tsirkin" wrote: > > > > > > > On Fri, Jul 24, 2020 at 04:56:27PM +0200, Cornelia Huck wrote: > > > > > > > > On Fri, 24 Jul 2020 09:30:58 -0400 > > > > > > > > "Michael S. Tsirkin" wrote: > > > > > > > > > On Fri, Jul 24, 2020 at 03:27:18PM +0200, Cornelia Huck wrote: > > > > > > > > > > When I start qemu with a second virtio-net-ccw device (i.e. adding > > > > > > > > > > -device virtio-net-ccw in addition to the autogenerated device), I get > > > > > > > > > > a segfault. gdb points to > > > > > > > > > > > > > > > > > > > > #0 0x000055d6ab52681d in virtio_net_get_config (vdev=, > > > > > > > > > > config=0x55d6ad9e3f80 "RT") at /home/cohuck/git/qemu/hw/net/virtio-net.c:146 > > > > > > > > > > 146 if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > > > > > > > > > > > > > > > > > > (backtrace doesn't go further) > > > > > > > > The core was incomplete, but running under gdb directly shows that it > > > > > > > > is just a bog-standard config space access (first for that device). > > > > > > > > > > > > > > > > The cause of the crash is that nc->peer is not set... no idea how that > > > > > > > > can happen, not that familiar with that part of QEMU. (Should the code > > > > > > > > check, or is that really something that should not happen?) > > > > > > > > > > > > > > > > What I don't understand is why it is set correctly for the first, > > > > > > > > autogenerated virtio-net-ccw device, but not for the second one, and > > > > > > > > why virtio-net-pci doesn't show these problems. The only difference > > > > > > > > between -ccw and -pci that comes to my mind here is that config space > > > > > > > > accesses for ccw are done via an asynchronous operation, so timing > > > > > > > > might be different. > > > > > > > Hopefully Jason has an idea. Could you post a full command line > > > > > > > please? Do you need a working guest to trigger this? Does this trigger > > > > > > > on an x86 host? > > > > > > Yes, it does trigger with tcg-on-x86 as well. I've been using > > > > > > > > > > > > s390x-softmmu/qemu-system-s390x -M s390-ccw-virtio,accel=tcg -cpu qemu,zpci=on > > > > > > -m 1024 -nographic -device virtio-scsi-ccw,id=scsi0,devno=fe.0.0001 > > > > > > -drive file=/path/to/image,format=qcow2,if=none,id=drive-scsi0-0-0-0 > > > > > > -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1 > > > > > > -device virtio-net-ccw > > > > > > > > > > > > It seems it needs the guest actually doing something with the nics; I > > > > > > cannot reproduce the crash if I use the old advent calendar moon buggy > > > > > > image and just add a virtio-net-ccw device. > > > > > > > > > > > > (I don't think it's a problem with my local build, as I see the problem > > > > > > both on my laptop and on an LPAR.) > > > > > It looks to me we forget the check the existence of peer. > > > > > > > > > > Please try the attached patch to see if it works. > > > > Thanks, that patch gets my guest up and running again. So, FWIW, > > > > > > > > Tested-by: Cornelia Huck > > > > > > > > Any idea why this did not hit with virtio-net-pci (or the autogenerated > > > > virtio-net-ccw device)? > > > > > > It can be hit with virtio-net-pci as well (just start without peer). > > Hm, I had not been able to reproduce the crash with a 'naked' -device > > virtio-net-pci. But checking seems to be the right idea anyway. > > > Sorry for being unclear, I meant for networking part, you just need start > without peer, and you need a real guest (any Linux) that is trying to access > the config space of virtio-net. > > Thanks A pxe guest will do it, but that doesn't support ccw, right? I'm still unclear why this triggers with ccw but not pci - any idea? > > > > > > For autogenerated virtio-net-cww, I think the reason is that it has > > > already had a peer set. > > Ok, that might well be. > > > >