From: Bobby Eshleman <bobbyeshleman@meta.com>

Add NS support to vsock loopback. Sockets in a global mode netns
communicate with each other, regardless of namespace. Sockets in a local
mode netns may only communicate with other sockets within the same
namespace.

Use pernet_ops to install a vsock_loopback for every namespace that is
created (to be used if local mode is enabled).

Retroactively call init/exit on every namespace when the vsock_loopback
module is loaded in order to initialize the per-ns device.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
Changes in v7:
- drop for_each_net() init/exit, drop net_rwsem, the pernet registration
  handles this automatically and race-free
- flush workqueue before destruction, purge pkt list
- remember net_mode instead of current net mode
- keep space after INIT_WORK()
- change vsock_loopback in netns_vsock to ->priv void ptr
- rename `orig_net_mode` to `net_mode`
- remove useless comment
- protect `register_pernet_subsys()` with `net_rwsem`
- do cleanup before releasing `net_rwsem` when failure happens
- call `unregister_pernet_subsys()` in `vsock_loopback_exit()`
- call `vsock_loopback_deinit_vsock()` in `vsock_loopback_exit()`

Changes in v6:
- init pernet ops for vsock_loopback module
- vsock_loopback: add space in struct to clarify lock protection
- do proper cleanup/unregister on vsock_loopback_exit()
- vsock_loopback: use virtio_vsock_skb_net()

Changes in v5:
- add callbacks code to avoid reverse dependency
- add logic for handling vsock_loopback setup for already existing
  namespaces
---
 include/net/netns/vsock.h      |  2 +
 net/vmw_vsock/vsock_loopback.c | 85 ++++++++++++++++++++++++++++++++++++------
 2 files changed, 75 insertions(+), 12 deletions(-)

diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
index c9a438ad52f2..9d0d8e2fbc37 100644
--- a/include/net/netns/vsock.h
+++ b/include/net/netns/vsock.h
@@ -16,5 +16,7 @@ struct netns_vsock {
 	/* protected by lock */
 	enum vsock_net_mode mode;
 	bool mode_locked;
+
+	void *priv;
 };
 #endif /* __NET_NET_NAMESPACE_VSOCK_H */
diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
index a8f218f0c5a3..474083d4cfcb 100644
--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -28,8 +28,16 @@ static u32 vsock_loopback_get_local_cid(void)
 
 static int vsock_loopback_send_pkt(struct sk_buff *skb)
 {
-	struct vsock_loopback *vsock = &the_vsock_loopback;
+	struct vsock_loopback *vsock;
 	int len = skb->len;
+	struct net *net;
+
+	net = virtio_vsock_skb_net(skb);
+
+	if (virtio_vsock_skb_net_mode(skb) == VSOCK_NET_MODE_LOCAL)
+		vsock = (struct vsock_loopback *)net->vsock.priv;
+	else
+		vsock = &the_vsock_loopback;
 
 	virtio_vsock_skb_queue_tail(&vsock->pkt_queue, skb);
 	queue_work(vsock->workqueue, &vsock->pkt_work);
@@ -134,11 +142,8 @@ static void vsock_loopback_work(struct work_struct *work)
 	}
 }
 
-static int __init vsock_loopback_init(void)
+static int vsock_loopback_init_vsock(struct vsock_loopback *vsock)
 {
-	struct vsock_loopback *vsock = &the_vsock_loopback;
-	int ret;
-
 	vsock->workqueue = alloc_workqueue("vsock-loopback", WQ_PERCPU, 0);
 	if (!vsock->workqueue)
 		return -ENOMEM;
@@ -146,15 +151,73 @@ static int __init vsock_loopback_init(void)
 	skb_queue_head_init(&vsock->pkt_queue);
 	INIT_WORK(&vsock->pkt_work, vsock_loopback_work);
 
+	return 0;
+}
+
+static void vsock_loopback_deinit_vsock(struct vsock_loopback *vsock)
+{
+	if (vsock->workqueue) {
+		flush_work(&vsock->pkt_work);
+		virtio_vsock_skb_queue_purge(&vsock->pkt_queue);
+		destroy_workqueue(vsock->workqueue);
+		vsock->workqueue = NULL;
+	}
+}
+
+static int vsock_loopback_init_net(struct net *net)
+{
+	int ret;
+
+	net->vsock.priv = kzalloc(sizeof(struct vsock_loopback), GFP_KERNEL);
+	if (!net->vsock.priv)
+		return -ENOMEM;
+
+	ret = vsock_loopback_init_vsock((struct vsock_loopback *)net->vsock.priv);
+	if (ret < 0) {
+		kfree(net->vsock.priv);
+		net->vsock.priv = NULL;
+		return ret;
+	}
+
+	return 0;
+}
+
+static void vsock_loopback_exit_net(struct net *net)
+{
+	vsock_loopback_deinit_vsock(net->vsock.priv);
+	kfree(net->vsock.priv);
+	net->vsock.priv = NULL;
+}
+
+static struct pernet_operations vsock_loopback_net_ops = {
+	.init = vsock_loopback_init_net,
+	.exit = vsock_loopback_exit_net,
+};
+
+static int __init vsock_loopback_init(void)
+{
+	struct vsock_loopback *vsock = &the_vsock_loopback;
+	int ret;
+
+	ret = vsock_loopback_init_vsock(vsock);
+	if (ret < 0)
+		return ret;
+
+	ret = register_pernet_subsys(&vsock_loopback_net_ops);
+	if (ret < 0)
+		goto out_deinit_vsock;
+
 	ret = vsock_core_register(&loopback_transport.transport,
 				  VSOCK_TRANSPORT_F_LOCAL);
 	if (ret)
-		goto out_wq;
+		goto out_unregister_pernet_subsys;
 
 	return 0;
 
-out_wq:
-	destroy_workqueue(vsock->workqueue);
+out_unregister_pernet_subsys:
+	unregister_pernet_subsys(&vsock_loopback_net_ops);
+out_deinit_vsock:
+	vsock_loopback_deinit_vsock(vsock);
 	return ret;
 }
 
@@ -164,11 +227,9 @@ static void __exit vsock_loopback_exit(void)
 
 	vsock_core_unregister(&loopback_transport.transport);
 
-	flush_work(&vsock->pkt_work);
-
-	virtio_vsock_skb_queue_purge(&vsock->pkt_queue);
+	unregister_pernet_subsys(&vsock_loopback_net_ops);
 
-	destroy_workqueue(vsock->workqueue);
+	vsock_loopback_deinit_vsock(vsock);
 }
 
 module_init(vsock_loopback_init);

-- 
2.47.3

On Thu, Oct 23, 2025 at 11:27:44AM -0700, Bobby Eshleman wrote:
>From: Bobby Eshleman <bobbyeshleman@meta.com>
>
>Add NS support to vsock loopback. Sockets in a global mode netns
>communicate with each other, regardless of namespace. Sockets in a local
>mode netns may only communicate with other sockets within the same
>namespace.
>
>Use pernet_ops to install a vsock_loopback for every namespace that is
>created (to be used if local mode is enabled).
>
>Retroactively call init/exit on every namespace when the vsock_loopback
>module is loaded in order to initialize the per-ns device.
>
>Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
>---

I'm a bit confused, should we move this after the next patch that add 
support of netns in the virtio common module?

Or this is a pre-requisite?

>Changes in v7:
>- drop for_each_net() init/exit, drop net_rwsem, the pernet registration
>  handles this automatically and race-free
>- flush workqueue before destruction, purge pkt list
>- remember net_mode instead of current net mode
>- keep space after INIT_WORK()
>- change vsock_loopback in netns_vsock to ->priv void ptr
>- rename `orig_net_mode` to `net_mode`
>- remove useless comment
>- protect `register_pernet_subsys()` with `net_rwsem`
>- do cleanup before releasing `net_rwsem` when failure happens
>- call `unregister_pernet_subsys()` in `vsock_loopback_exit()`
>- call `vsock_loopback_deinit_vsock()` in `vsock_loopback_exit()`
>
>Changes in v6:
>- init pernet ops for vsock_loopback module
>- vsock_loopback: add space in struct to clarify lock protection
>- do proper cleanup/unregister on vsock_loopback_exit()
>- vsock_loopback: use virtio_vsock_skb_net()
>
>Changes in v5:
>- add callbacks code to avoid reverse dependency
>- add logic for handling vsock_loopback setup for already existing
>  namespaces
>---
> include/net/netns/vsock.h      |  2 +
> net/vmw_vsock/vsock_loopback.c | 85 ++++++++++++++++++++++++++++++++++++------
> 2 files changed, 75 insertions(+), 12 deletions(-)
>
>diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
>index c9a438ad52f2..9d0d8e2fbc37 100644
>--- a/include/net/netns/vsock.h
>+++ b/include/net/netns/vsock.h
>@@ -16,5 +16,7 @@ struct netns_vsock {
> 	/* protected by lock */
> 	enum vsock_net_mode mode;
> 	bool mode_locked;
>+
>+	void *priv;
> };
> #endif /* __NET_NET_NAMESPACE_VSOCK_H */
>diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
>index a8f218f0c5a3..474083d4cfcb 100644
>--- a/net/vmw_vsock/vsock_loopback.c
>+++ b/net/vmw_vsock/vsock_loopback.c
>@@ -28,8 +28,16 @@ static u32 vsock_loopback_get_local_cid(void)
>
> static int vsock_loopback_send_pkt(struct sk_buff *skb)
> {
>-	struct vsock_loopback *vsock = &the_vsock_loopback;
>+	struct vsock_loopback *vsock;
> 	int len = skb->len;
>+	struct net *net;
>+
>+	net = virtio_vsock_skb_net(skb);
>+
>+	if (virtio_vsock_skb_net_mode(skb) == VSOCK_NET_MODE_LOCAL)
>+		vsock = (struct vsock_loopback *)net->vsock.priv;

Is there some kind of refcount on the net?
What I mean is, are we sure this pointer is still valid? Could the net 
disappear in the meantime?

The rest LGTM!

Thanks,
Stefano

>+	else
>+		vsock = &the_vsock_loopback;
>
> 	virtio_vsock_skb_queue_tail(&vsock->pkt_queue, skb);
> 	queue_work(vsock->workqueue, &vsock->pkt_work);
>@@ -134,11 +142,8 @@ static void vsock_loopback_work(struct work_struct *work)
> 	}
> }
>
>-static int __init vsock_loopback_init(void)
>+static int vsock_loopback_init_vsock(struct vsock_loopback *vsock)
> {
>-	struct vsock_loopback *vsock = &the_vsock_loopback;
>-	int ret;
>-
> 	vsock->workqueue = alloc_workqueue("vsock-loopback", WQ_PERCPU, 0);
> 	if (!vsock->workqueue)
> 		return -ENOMEM;
>@@ -146,15 +151,73 @@ static int __init vsock_loopback_init(void)
> 	skb_queue_head_init(&vsock->pkt_queue);
> 	INIT_WORK(&vsock->pkt_work, vsock_loopback_work);
>
>+	return 0;
>+}
>+
>+static void vsock_loopback_deinit_vsock(struct vsock_loopback *vsock)
>+{
>+	if (vsock->workqueue) {
>+		flush_work(&vsock->pkt_work);
>+		virtio_vsock_skb_queue_purge(&vsock->pkt_queue);
>+		destroy_workqueue(vsock->workqueue);
>+		vsock->workqueue = NULL;
>+	}
>+}
>+
>+static int vsock_loopback_init_net(struct net *net)
>+{
>+	int ret;
>+
>+	net->vsock.priv = kzalloc(sizeof(struct vsock_loopback), GFP_KERNEL);
>+	if (!net->vsock.priv)
>+		return -ENOMEM;
>+
>+	ret = vsock_loopback_init_vsock((struct vsock_loopback *)net->vsock.priv);
>+	if (ret < 0) {
>+		kfree(net->vsock.priv);
>+		net->vsock.priv = NULL;
>+		return ret;
>+	}
>+
>+	return 0;
>+}
>+
>+static void vsock_loopback_exit_net(struct net *net)
>+{
>+	vsock_loopback_deinit_vsock(net->vsock.priv);
>+	kfree(net->vsock.priv);
>+	net->vsock.priv = NULL;
>+}
>+
>+static struct pernet_operations vsock_loopback_net_ops = {
>+	.init = vsock_loopback_init_net,
>+	.exit = vsock_loopback_exit_net,
>+};
>+
>+static int __init vsock_loopback_init(void)
>+{
>+	struct vsock_loopback *vsock = &the_vsock_loopback;
>+	int ret;
>+
>+	ret = vsock_loopback_init_vsock(vsock);
>+	if (ret < 0)
>+		return ret;
>+
>+	ret = register_pernet_subsys(&vsock_loopback_net_ops);
>+	if (ret < 0)
>+		goto out_deinit_vsock;
>+
> 	ret = vsock_core_register(&loopback_transport.transport,
> 				  VSOCK_TRANSPORT_F_LOCAL);
> 	if (ret)
>-		goto out_wq;
>+		goto out_unregister_pernet_subsys;
>
> 	return 0;
>
>-out_wq:
>-	destroy_workqueue(vsock->workqueue);
>+out_unregister_pernet_subsys:
>+	unregister_pernet_subsys(&vsock_loopback_net_ops);
>+out_deinit_vsock:
>+	vsock_loopback_deinit_vsock(vsock);
> 	return ret;
> }
>
>@@ -164,11 +227,9 @@ static void __exit vsock_loopback_exit(void)
>
> 	vsock_core_unregister(&loopback_transport.transport);
>
>-	flush_work(&vsock->pkt_work);
>-
>-	virtio_vsock_skb_queue_purge(&vsock->pkt_queue);
>+	unregister_pernet_subsys(&vsock_loopback_net_ops);
>
>-	destroy_workqueue(vsock->workqueue);
>+	vsock_loopback_deinit_vsock(vsock);
> }
>
> module_init(vsock_loopback_init);
>
>-- 
>2.47.3
>

On Thu, Nov 06, 2025 at 05:18:36PM +0100, Stefano Garzarella wrote:
> On Thu, Oct 23, 2025 at 11:27:44AM -0700, Bobby Eshleman wrote:
> > From: Bobby Eshleman <bobbyeshleman@meta.com>
> > 
> > Add NS support to vsock loopback. Sockets in a global mode netns
> > communicate with each other, regardless of namespace. Sockets in a local
> > mode netns may only communicate with other sockets within the same
> > namespace.
> > 
> > Use pernet_ops to install a vsock_loopback for every namespace that is
> > created (to be used if local mode is enabled).
> > 
> > Retroactively call init/exit on every namespace when the vsock_loopback
> > module is loaded in order to initialize the per-ns device.
> > 
> > Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
> > ---
> 
> I'm a bit confused, should we move this after the next patch that add
> support of netns in the virtio common module?
> 
> Or this is a pre-requisite?
> 

Yes let's do that, it does need common.

[...]

> > #endif /* __NET_NET_NAMESPACE_VSOCK_H */
> > diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> > index a8f218f0c5a3..474083d4cfcb 100644
> > --- a/net/vmw_vsock/vsock_loopback.c
> > +++ b/net/vmw_vsock/vsock_loopback.c
> > @@ -28,8 +28,16 @@ static u32 vsock_loopback_get_local_cid(void)
> > 
> > static int vsock_loopback_send_pkt(struct sk_buff *skb)
> > {
> > -	struct vsock_loopback *vsock = &the_vsock_loopback;
> > +	struct vsock_loopback *vsock;
> > 	int len = skb->len;
> > +	struct net *net;
> > +
> > +	net = virtio_vsock_skb_net(skb);
> > +
> > +	if (virtio_vsock_skb_net_mode(skb) == VSOCK_NET_MODE_LOCAL)
> > +		vsock = (struct vsock_loopback *)net->vsock.priv;
> 
> Is there some kind of refcount on the net?
> What I mean is, are we sure this pointer is still valid? Could the net
> disappear in the meantime?

I only considered the case of net being removed, which I think is okay
because user sockets take a net reference in sk_alloc(), and we can't
reach this point after the sock is destroyed and the reference is
released because the transport will be unassigned prior.

But... I'm now realizing there is the case of
virtio_transport_reset_no_sock() where skb net is null. I can't see why
that wouldn't be possible for loopback?

Let's handle that case to be sure...

> 
> The rest LGTM!
> 
> Thanks, Stefano
> 

Best,
Bobby