From 16f6804c460109e8b126cc710a0072f9f83bd230 Mon Sep 17 00:00:00 2001 From: zuoboqun Date: Fri, 15 Nov 2024 16:03:12 +0800 Subject: [PATCH] vhost_net: fix assertion triggered by batch of host notifiers processing When the backend of vhost_net restarts during the vm is running, vhost_net is stopped and started. The virtio_device_grab_ioeventfd() fucntion in vhost_net_enable_notifiers() will result in a call to virtio_bus_set_host_notifier()(assign=false). And now virtio_device_grab_ioeventfd() is batched in a single transaction with virtio_bus_set_host_notifier()(assign=true). This triggers the following assertion: kvm_mem_ioeventfd_del: error deleting ioeventfd: Bad file descriptor This patch moves virtio_device_grab_ioeventfd() out of the batch to fix this problem. To be noted that the for loop to release ioeventfd should start from i+1, not i, because the i-th ioeventfd has already been released in vhost_dev_disable_notifiers_nvqs(). Fixes: 6166799f6 ("vhost_net: configure all host notifiers in a single MR transaction") Signed-off-by: Zuo Boqun Reported-by: Gao Shiyuan Message-Id: <20241115080312.3184-1-zuoboqun@baidu.com> Acked-by: Stefano Garzarella Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- hw/net/vhost_net.c | 35 ++++++++++++++++++++++++----------- 1 file changed, 24 insertions(+), 11 deletions(-) diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c index 997aab0557..891f235a0a 100644 --- a/hw/net/vhost_net.c +++ b/hw/net/vhost_net.c @@ -229,9 +229,24 @@ static int vhost_net_enable_notifiers(VirtIODevice *dev, int nvhosts = data_queue_pairs + cvq; struct vhost_net *net; struct vhost_dev *hdev; - int r, i, j; + int r, i, j, k; NetClientState *peer; + /* + * We will pass the notifiers to the kernel, make sure that QEMU + * doesn't interfere. + */ + for (i = 0; i < nvhosts; i++) { + r = virtio_device_grab_ioeventfd(dev); + if (r < 0) { + error_report("vhost %d binding does not support host notifiers", i); + for (k = 0; k < i; k++) { + virtio_device_release_ioeventfd(dev); + } + return r; + } + } + /* * Batch all the host notifiers in a single transaction to avoid * quadratic time complexity in address_space_update_ioeventfds(). @@ -247,16 +262,6 @@ static int vhost_net_enable_notifiers(VirtIODevice *dev, net = get_vhost_net(peer); hdev = &net->dev; - /* - * We will pass the notifiers to the kernel, make sure that QEMU - * doesn't interfere. - */ - r = virtio_device_grab_ioeventfd(dev); - if (r < 0) { - error_report("binding does not support host notifiers"); - memory_region_transaction_commit(); - goto fail_nvhosts; - } for (j = 0; j < hdev->nvqs; j++) { r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), @@ -277,6 +282,14 @@ static int vhost_net_enable_notifiers(VirtIODevice *dev, return 0; fail_nvhosts: vhost_net_disable_notifiers_nvhosts(dev, ncs, data_queue_pairs, i); + /* + * This for loop starts from i+1, not i, because the i-th ioeventfd + * has already been released in vhost_dev_disable_notifiers_nvqs(). + */ + for (k = i + 1; k < nvhosts; k++) { + virtio_device_release_ioeventfd(dev); + } + return r; } -- 2.30.2