From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58374) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eSSNg-0004zI-Mb for qemu-devel@nongnu.org; Fri, 22 Dec 2017 13:49:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eSSNd-00081n-JG for qemu-devel@nongnu.org; Fri, 22 Dec 2017 13:49:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50268) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eSSNd-00080i-8t for qemu-devel@nongnu.org; Fri, 22 Dec 2017 13:49:13 -0500 Date: Fri, 22 Dec 2017 19:48:55 +0100 From: Igor Mammedov Message-ID: <20171222194855.6d1139f1@igors-macbook-pro.local> In-Reply-To: <1513327555-17520-3-git-send-email-jianjay.zhou@huawei.com> References: <1513327555-17520-1-git-send-email-jianjay.zhou@huawei.com> <1513327555-17520-3-git-send-email-jianjay.zhou@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jay Zhou Cc: qemu-devel@nongnu.org, mst@redhat.com, weidong.huang@huawei.com, arei.gonglei@huawei.com, wangxinxin.wang@huawei.com, gary.liuzhe@huawei.com, dgilbert@redhat.com On Fri, 15 Dec 2017 16:45:55 +0800 Jay Zhou wrote: > If the VM already has N(N>8) available memory slots for vhost user, > the VM will be crashed in vhost_user_set_mem_table if we try to > hotplug the first vhost user NIC. > This patch checks if memslots number exceeded or not after updating > vhost_user_used_memslots. Can't understand commit message, pls rephrase (what is being fixed, and how it's fixed) also include reproducing steps for crash and maybe describe call flow/backtrace that triggers crash. PS: I wasn't able to reproduce crash > > Signed-off-by: Jay Zhou > --- > hw/virtio/vhost.c | 27 +++++++++++++++++++++++---- > 1 file changed, 23 insertions(+), 4 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index 59a32e9..e45f5e2 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -1234,6 +1234,18 @@ static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq) > event_notifier_cleanup(&vq->masked_notifier); > } > > +static bool vhost_dev_used_memslots_is_exceeded(struct vhost_dev *hdev) > +{ > + if (hdev->vhost_ops->vhost_get_used_memslots() > > + hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) { > + error_report("vhost backend memory slots limit is less" > + " than current number of present memory slots"); > + return true; > + } > + > + return false; > +} > + > int vhost_dev_init(struct vhost_dev *hdev, void *opaque, > VhostBackendType backend_type, uint32_t busyloop_timeout) > { > @@ -1252,10 +1264,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque, > goto fail; > } > > - if (hdev->vhost_ops->vhost_get_used_memslots() > > - hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) { > - error_report("vhost backend memory slots limit is less" > - " than current number of present memory slots"); > + if (vhost_dev_used_memslots_is_exceeded(hdev)) { why do you keep this check? it seems always be false > r = -1; > goto fail; > } > @@ -1341,6 +1350,16 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque, > hdev->memory_changed = false; > memory_listener_register(&hdev->memory_listener, &address_space_memory); > QLIST_INSERT_HEAD(&vhost_devices, hdev, entry); > + > + if (vhost_dev_used_memslots_is_exceeded(hdev)) { > + r = -1; > + if (busyloop_timeout) { > + goto fail_busyloop; > + } else { > + goto fail; > + } > + } seem to be right thing to do, since after registering listener for the first time used_memslots will be updated to actual value. I did some testing and without this hunk/patch on 'device_add virtio-net-pci,netdev=net0' qemu prints: qemu-system-x86_64: vhost_set_mem_table failed: Argument list too long (7) qemu-system-x86_64: unable to start vhost net: 7: falling back on userspace virtio and network is operational in guest, but with this patch "netdev_add ...,vhost-on" prints: vhost backend memory slots limit is less than current number of present memory slots vhost-net requested but could not be initialized and following "device_add virtio-net-pci,netdev=net0" prints: TUNSETOFFLOAD ioctl() failed: Bad file descriptor TUNSETOFFLOAD ioctl() failed: Bad file descriptor adapter is still hot-plugged but guest networking is broken (can't get IP address via DHCP) so patch seems introduces a regression or something broken elsewhere and this exposes issue, not sure what qemu reaction should be in this case i.e. when netdev_add fails 1: should we fail followed up device_add or 2: make it fall back to userspace virtio I'd go for #2, Michael what's your take on it? > + > return 0; > > fail_busyloop: