linux-kernel - Re: [PATCH v3 3/9] vsock/virtio: Move length check to callers of virtio_vsock_skb_rx

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Message-ID: <ho6edx2uqqazyeoe3vm4oruas44ozngsoyhcuilremkzqg7u44@b6xeevkxtlmc>
Date: Tue, 15 Jul 2025 11:55:15 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org, Keir Fraser <keirf@...gle.com>, 
	Steven Moreland <smoreland@...gle.com>, Frederick Mayle <fmayle@...gle.com>, 
	Stefan Hajnoczi <stefanha@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
	Jason Wang <jasowang@...hat.com>, Eugenio Pérez <eperezma@...hat.com>, 
	netdev@...r.kernel.org, virtualization@...ts.linux.dev
Subject: Re: [PATCH v3 3/9] vsock/virtio: Move length check to callers of
 virtio_vsock_skb_rx_put()

On Mon, Jul 14, 2025 at 04:20:57PM +0100, Will Deacon wrote:
>virtio_vsock_skb_rx_put() only calls skb_put() if the length in the
>packet header is not zero even though skb_put() handles this case
>gracefully.
>
>Remove the functionally redundant check from virtio_vsock_skb_rx_put()
>and, on the assumption that this is a worthwhile optimisation for
>handling credit messages, augment the existing length checks in
>virtio_transport_rx_work() to elide the call for zero-length payloads.
>Since the callers all have the length, extend virtio_vsock_skb_rx_put()
>to take it as an additional parameter rather than fish it back out of
>the packet header.
>
>Note that the vhost code already has similar logic in
>vhost_vsock_alloc_skb().
>
>Signed-off-by: Will Deacon <will@...nel.org>
>---
> drivers/vhost/vsock.c            | 2 +-
> include/linux/virtio_vsock.h     | 9 ++-------
> net/vmw_vsock/virtio_transport.c | 4 +++-
> 3 files changed, 6 insertions(+), 9 deletions(-)

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 66a0f060770e..4c4a642945eb 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -375,7 +375,7 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
> 		return NULL;
> 	}
>
>-	virtio_vsock_skb_rx_put(skb);
>+	virtio_vsock_skb_rx_put(skb, payload_len);
>
> 	nbytes = copy_from_iter(skb->data, payload_len, &iov_iter);
> 	if (nbytes != payload_len) {
>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>index 36fb3edfa403..97465f378ade 100644
>--- a/include/linux/virtio_vsock.h
>+++ b/include/linux/virtio_vsock.h
>@@ -47,14 +47,9 @@ static inline void virtio_vsock_skb_clear_tap_delivered(struct sk_buff *skb)
> 	VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered = false;
> }
>
>-static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
>+static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb, u32 len)
> {
>-	u32 len;
>-
>-	len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
>-
>-	if (len > 0)
>-		skb_put(skb, len);
>+	skb_put(skb, len);
> }
>
> static inline struct sk_buff *virtio_vsock_alloc_skb(unsigned int size, gfp_t mask)
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index bd2c6aaa1a93..1af7723669cb 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -656,7 +656,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 				continue;
> 			}
>
>-			virtio_vsock_skb_rx_put(skb);
>+			if (payload_len)
>+				virtio_vsock_skb_rx_put(skb, payload_len);
>+
> 			virtio_transport_deliver_tap_pkt(skb);
> 			virtio_transport_recv_pkt(&virtio_transport, skb);
> 		}
>-- 
>2.50.0.727.gbf7dc18ff4-goog
>