On Thursday, November 14, 2024 6:54 PM, Stefano Garzarella wrote:
> >
> >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.
> >
> >Fixes: 6166799f6 ("vhost_net: configure all host notifiers in a single
> >MR transaction")
> >Reported-by: Gao Shiyuan <gaoshiy...@baidu.com>
> >Signed-off-by: Zuo Boqun <zuobo...@baidu.com>
> >---
> > hw/net/vhost_net.c | 31 ++++++++++++++++++++-----------
> > 1 file changed, 20 insertions(+), 11 deletions(-)
> >
> >diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c index
> >997aab0557..eb3e92ca0d 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 +282,10 @@ static int vhost_net_enable_notifiers(VirtIODevice
> *dev,
> > return 0;
> > fail_nvhosts:
> > vhost_net_disable_notifiers_nvhosts(dev, ncs, data_queue_pairs,
> >i);
>
> IIUC this call is disabling notifiers from 0 to `i - 1` ...
>
> >+ for (k = i + 1; k < nvhosts; k++) {
>
> ... so, should we start from `i`, instead of `i + 1`?
>
> Thanks,
> Stefano
The notifier `i` has been released when vhost_net_enable_notifiers() call
vhost_dev_disable_notifiers_nvqs():
for (j = 0; j < hdev->nvqs; j++) {
r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus),
hdev->vq_index + j,
true);
if (r < 0) {
error_report("vhost %d VQ %d notifier binding failed: %d",
i, j, -r);
memory_region_transaction_commit();
=> vhost_dev_disable_notifiers_nvqs(hdev, dev, j);
goto fail_nvhosts;
}
}
So we should start from `i+1`...
>
> >+ virtio_device_release_ioeventfd(dev);
> >+ }
> >+
> > return r;
> > }
> >
> >--
> >2.42.0.windows.2
> >
