linux-kernel - Re: [PATCH v2 3/8] vsock/virtio: Move length check to callers of virtio_vsock_skb_rx

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Message-ID: <g3h6k6vqfxwqsvojptaqy63qsn2vwo7i45segjgwjgmotysmwr@dmgbwacytag7>
Date: Wed, 2 Jul 2025 18:28:37 +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 v2 3/8] vsock/virtio: Move length check to callers of
 virtio_vsock_skb_rx_put()

On Tue, Jul 01, 2025 at 05:45:02PM +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.
>Note that the vhost code already has similar logic in
>vhost_vsock_alloc_skb().
>
>Signed-off-by: Will Deacon <will@...nel.org>
>---
> include/linux/virtio_vsock.h     | 4 +---
> net/vmw_vsock/virtio_transport.c | 4 +++-
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>index 36fb3edfa403..eb6980aa19fd 100644
>--- a/include/linux/virtio_vsock.h
>+++ b/include/linux/virtio_vsock.h
>@@ -52,9 +52,7 @@ static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
> 	u32 len;
>
> 	len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
>-
>-	if (len > 0)
>-		skb_put(skb, len);
>+	skb_put(skb, len);

Since the caller is supposed to check the len, can we just pass it as 
parameter?

So we can avoid the `le32_to_cpu(virtio_vsock_hdr(skb)->len)` here.

Thanks,
Stefano

> }
>
> 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..488e6ddc6ffa 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);
>+
> 			virtio_transport_deliver_tap_pkt(skb);
> 			virtio_transport_recv_pkt(&virtio_transport, skb);
> 		}
>-- 
>2.50.0.727.gbf7dc18ff4-goog
>