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[79.179.105.63]) by smtp.gmail.com with ESMTPSA id n189sm7724129wmf.38.2020.07.24.08.17.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Jul 2020 08:18:00 -0700 (PDT) Date: Fri, 24 Jul 2020 11:17:57 -0400 From: "Michael S. Tsirkin" To: Cornelia Huck Subject: Re: [BUG] vhost-vdpa: qemu-system-s390x crashes with second virtio-net-ccw device Message-ID: <20200724111512-mutt-send-email-mst@kernel.org> References: <20200724152718.4e1cbc9e.cohuck@redhat.com> <20200724092906-mutt-send-email-mst@kernel.org> <20200724165627.70c6dfd6.cohuck@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200724165627.70c6dfd6.cohuck@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii 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 = 2020/07/24 08:55:06 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_H4=-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, Jason Wang , qemu-devel@nongnu.org, Cindy Lu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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? > > > > > > Starting qemu with no additional "-device virtio-net-ccw" (i.e., only > > > the autogenerated virtio-net-ccw device is present) works. Specifying > > > several "-device virtio-net-pci" works as well. > > > > > > Things break with 1e0a84ea49b6 ("vhost-vdpa: introduce vhost-vdpa net > > > client"), 38140cc4d971 ("vhost_net: introduce set_config & get_config") > > > works (in-between state does not compile). > > > > Ouch. I didn't test all in-between states :( > > But I wish we had a 0-day instrastructure like kernel has, > > that catches things like that. > > Yep, that would be useful... so patchew only builds the complete series? > > > > > > This is reproducible with tcg as well. Same problem both with > > > --enable-vhost-vdpa and --disable-vhost-vdpa. > > > > > > Have not yet tried to figure out what might be special with > > > virtio-ccw... anyone have an idea? > > > > > > [This should probably be considered a blocker?] > > I think so, as it makes s390x unusable with more that one > virtio-net-ccw device, and I don't even see a workaround.