On Fri, Nov 15, 2024 at 04:03:12PM +0800, Zuo boqun wrote:
From: zuoboqun <zuobo...@baidu.com>
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 <zuobo...@baidu.com>
Reported-by: Gao Shiyuan <gaoshiy...@baidu.com>
---
v1->v2:
*To explain why the for loop to release ioeventfd starts from i+1:
1) add a comment in the code
2) describe it in the commit message
Thanks for that!
LGTM, but I don't know vhost-net enough so I'd wait for a comment from
Michael and Jason.
Acked-by: Stefano Garzarella <sgarz...@redhat.com>
---
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;
}
--
2.42.0.windows.2
