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[82.53.134.58]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483bfcbf8b6sm147619295e9.20.2026.03.02.03.47.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2026 03:47:11 -0800 (PST) Date: Mon, 2 Mar 2026 12:47:05 +0100 From: Stefano Garzarella To: Alexander Graf Cc: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, kvm@vger.kernel.org, eperezma@redhat.com, Jason Wang , mst@redhat.com, Stefan Hajnoczi , nh-open-source@amazon.com Subject: Re: [PATCH] vsock: Enable H2G override Message-ID: References: <20260302104138.77555-1-graf@amazon.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260302104138.77555-1-graf@amazon.com> Please target net-next tree for this new feature. On Mon, Mar 02, 2026 at 10:41:38AM +0000, Alexander Graf wrote: >Vsock maintains a single CID number space which can be used to >communicate to the host (G2H) or to a child-VM (H2G). The current logic >trivially assumes that G2H is only relevant for CID <= 2 because these >target the hypervisor. However, in environments like Nitro Enclaves, an >instance that hosts vhost_vsock powered VMs may still want to communicate >to Enclaves that are reachable at higher CIDs through virtio-vsock-pci. > >That means that for CID > 2, we really want an overlay. By default, all >CIDs are owned by the hypervisor. But if vhost registers a CID, it takes >precedence. Implement that logic. Vhost already knows which CIDs it >supports anyway. > >With this logic, I can run a Nitro Enclave as well as a nested VM with >vhost-vsock support in parallel, with the parent instance able to >communicate to both simultaneously. I honestly don't understand why VMADDR_FLAG_TO_HOST (added specifically for Nitro IIRC) isn't enough for this scenario and we have to add this change. Can you elaborate a bit more about the relationship between this change and VMADDR_FLAG_TO_HOST we added? > >Signed-off-by: Alexander Graf >--- > drivers/vhost/vsock.c | 11 +++++++++++ > include/net/af_vsock.h | 3 +++ > net/vmw_vsock/af_vsock.c | 3 +++ > 3 files changed, 17 insertions(+) > >diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c >index 054f7a718f50..223da817e305 100644 >--- a/drivers/vhost/vsock.c >+++ b/drivers/vhost/vsock.c >@@ -91,6 +91,16 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid, struct net *net) > return NULL; > } > >+static bool vhost_transport_has_cid(u32 cid) >+{ >+ bool found; >+ >+ rcu_read_lock(); >+ found = vhost_vsock_get(cid) != NULL; We recently added namespaces support that changed vhost_vsock_get() params. This is also in net tree now and in Linus' tree, so not sure where this patch is based, but this needs to be rebased since it is not building: ../drivers/vhost/vsock.c: In function ‘vhost_transport_has_cid’: ../drivers/vhost/vsock.c:99:17: error: too few arguments to function ‘vhost_vsock_get’; expected 2, have 1 99 | found = vhost_vsock_get(cid) != NULL; | ^~~~~~~~~~~~~~~ ../drivers/vhost/vsock.c:74:28: note: declared here 74 | static struct vhost_vsock *vhost_vsock_get(u32 guest_cid, struct net *net) | >+ rcu_read_unlock(); >+ return found; >+} >+ > static void > vhost_transport_do_send_pkt(struct vhost_vsock *vsock, > struct vhost_virtqueue *vq) >@@ -424,6 +434,7 @@ static struct virtio_transport vhost_transport = { > .module = THIS_MODULE, > > .get_local_cid = vhost_transport_get_local_cid, >+ .has_cid = vhost_transport_has_cid, > > .init = virtio_transport_do_socket_init, > .destruct = virtio_transport_destruct, >diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h >index 533d8e75f7bb..4cdcb72f9765 100644 >--- a/include/net/af_vsock.h >+++ b/include/net/af_vsock.h >@@ -179,6 +179,9 @@ struct vsock_transport { > /* Addressing. */ > u32 (*get_local_cid)(void); > >+ /* Check if this transport serves a specific remote CID. */ >+ bool (*has_cid)(u32 cid); What about "has_remote_cid" ? >+ > /* Read a single skb */ > int (*read_skb)(struct vsock_sock *, skb_read_actor_t); > >diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c >index 2f7d94d682cb..8b34b264b246 100644 >--- a/net/vmw_vsock/af_vsock.c >+++ b/net/vmw_vsock/af_vsock.c >@@ -584,6 +584,9 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) > else if (remote_cid <= VMADDR_CID_HOST || !transport_h2g || > (remote_flags & VMADDR_FLAG_TO_HOST)) > new_transport = transport_g2h; >+ else if (transport_h2g->has_cid && >+ !transport_h2g->has_cid(remote_cid)) >+ new_transport = transport_g2h; We should update the comment on top of this fuction, and maybe also try to support the other H2G transport (i.e. VMCI). @Bryan @Vishnu can the new has_cid()/has_remote_cid() be supported by VMCI too? I have a question: until now, transport assignment was based simply on analyzing local socket information (vsk->remote_addr), but now we are also adding the status of other components (e.g., VMs that have started and registered the CID in vhost-vsock). Could this produce strange behavior? For example, two sockets with the same remote_addr communicate with the host or with the guest depending on whether or not the VM existed when they were created. Thanks, Stefano > else > new_transport = transport_h2g; > break; >-- >2.47.1 > > > > >Amazon Web Services Development Center Germany GmbH >Tamara-Danz-Str. 13 >10243 Berlin >Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger >Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B >Sitz: Berlin >Ust-ID: DE 365 538 597 > >