netdev - Re: [PATCH] vhost/vsock: reset only the h2g connections upon release

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Date:   Thu, 10 Mar 2022 09:59:31 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jiyong Park <jiyong@...gle.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, adelva@...gle.com,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost/vsock: reset only the h2g connections upon release

Hi Jiyong,

On Thu, Mar 10, 2022 at 05:18:54PM +0900, Jiyong Park wrote:
>Filtering non-h2g connections out when determining orphaned connections.
>Otherwise, in a nested VM configuration, destroying the nested VM (which
>often involves the closing of /dev/vhost-vsock if there was h2g
>connections to the nested VM) kills not only the h2g connections, but
>also all existing g2h connections to the (outmost) host which are
>totally unrelated.
>
>Tested: Executed the following steps on Cuttlefish (Android running on a
>VM) [1]: (1) Enter into an `adb shell` session - to have a g2h
>connection inside the VM, (2) open and then close /dev/vhost-vsock by
>`exec 3< /dev/vhost-vsock && exec 3<&-`, (3) observe that the adb
>session is not reset.
>
>[1] https://android.googlesource.com/device/google/cuttlefish/
>
>Signed-off-by: Jiyong Park <jiyong@...gle.com>
>---
> drivers/vhost/vsock.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 37f0b4274113..2f6d5d66f5ed 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -722,6 +722,10 @@ static void vhost_vsock_reset_orphans(struct sock *sk)
> 	 * executing.
> 	 */
>
>+	/* Only the h2g connections are reset */
>+	if (vsk->transport != &vhost_transport.transport)
>+		return;
>+
> 	/* If the peer is still valid, no need to reset connection */
> 	if (vhost_vsock_get(vsk->remote_addr.svm_cid))
> 		return;
>-- 
>2.35.1.723.g4982287a31-goog
>

Thanks for your patch!

Yes, I see the problem and I think I introduced it with the 
multi-transports support (ooops).

So we should add this fixes tag:

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")


IIUC the problem is for all transports that should only cycle on their 
own sockets. Indeed I think there is the same problem if the g2h driver 
will be unloaded (or a reset event is received after a VM migration), it 
will close all sockets of the nested h2g.

So I suggest a more generic solution, modifying 
vsock_for_each_connected_socket() like this (not tested):

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 38baeb189d4e..f04abf662ec6 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -334,7 +334,8 @@ void vsock_remove_sock(struct vsock_sock *vsk)
  }
  EXPORT_SYMBOL_GPL(vsock_remove_sock);

-void vsock_for_each_connected_socket(void (*fn)(struct sock *sk))
+void vsock_for_each_connected_socket(struct vsock_transport *transport,
+                                    void (*fn)(struct sock *sk))
  {
         int i;

@@ -343,8 +344,12 @@ void vsock_for_each_connected_socket(void (*fn)(struct sock *sk))
         for (i = 0; i < ARRAY_SIZE(vsock_connected_table); i++) {
                 struct vsock_sock *vsk;
                 list_for_each_entry(vsk, &vsock_connected_table[i],
-                                   connected_table)
+                                   connected_table) {
+                       if (vsk->transport != transport)
+                               continue;
+
                         fn(sk_vsock(vsk));
+               }
         }


And all transports that call it.

Thanks,
Stefano