Re: [PATCH net] Revert "vsock/virtio: fix skb overhead overflow on 32-bit builds"

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 27, 2026 at 06:54:21PM +0200, Stefano Garzarella wrote:
> On Wed, May 27, 2026 at 06:48:43PM +0200, Stefano Garzarella wrote:
> > From: Stefano Garzarella <sgarzare@redhat.com>
> > 
> > This reverts commit 4157501b9a8f ("vsock/virtio: fix skb overhead
> > overflow on 32-bit builds"). The fix was semantically correct (although
> > it would have been better to use mul_u32_u32(), as David pointed out),
> > but in practice we are estimating the memory used to allocate the SKBs,
> > and this will never cause a 32-bit variable to overflow on a 32-bit
> > system, since the memory would have run out long before that. On 64-bit,
> > SKB_TRUESIZE() already evaluates to size_t, so the multiplication is
> > already in 64-bit arithmetic without the cast.
> > 
> > Let's revert this to avoid unnecessary 64-bit multiplies on the
> > per-packet receive path on 32-bit systems.
> > 
> > Reported-by: David Laight <david.laight.linux@gmail.com>
> > Closes: https://lore.kernel.org/netdev/20260523173557.5cc4f4f6@pumpkin
> > Suggested-by: "Michael S. Tsirkin" <mst@redhat.com>
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> > ---
> > net/vmw_vsock/virtio_transport_common.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> aaarg, something wrong on my new setup, CC list was missing several people
> and mailing lists, including LKML. Please let me know if I should resend
> this.
> 
> Sorry for the noise,
> Stefano


yea just do it. Put PATCH resend in the subj.

> > 
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index b143290a311d..d4d26fba9e37 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -417,7 +417,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> > 					u32 len)
> > {
> > -	u64 skb_overhead = ((u64)skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
> > +	u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
> > 
> > 	/* Allow at most buf_alloc * 2 total budget (payload + overhead),
> > 	 * similar to how SO_RCVBUF is doubled to reserve space for sk_buff
> > -- 
> > 2.54.0
> >