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Wed, 27 May 2026 09:49:41 -0700 (PDT) X-Received: by 2002:a05:6000:40db:b0:45e:df08:b02 with SMTP id ffacd0b85a97d-45edf080c6dmr3334522f8f.28.1779900581419; Wed, 27 May 2026 09:49:41 -0700 (PDT) Received: from redhat.com ([31.187.78.155]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45edb54959bsm7881042f8f.1.2026.05.27.09.49.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 May 2026 09:49:40 -0700 (PDT) Date: Wed, 27 May 2026 12:49:38 -0400 From: "Michael S. Tsirkin" To: Stefano Garzarella Cc: netdev@vger.kernel.org, David Laight Subject: Re: [PATCH net] Revert "vsock/virtio: fix skb overhead overflow on 32-bit builds" Message-ID: <20260527124929-mutt-send-email-mst@kernel.org> References: <20260527164843.125054-1-sgarzare@redhat.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260527164843.125054-1-sgarzare@redhat.com> On Wed, May 27, 2026 at 06:48:43PM +0200, Stefano Garzarella wrote: > From: Stefano Garzarella > > 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 > Closes: https://lore.kernel.org/netdev/20260523173557.5cc4f4f6@pumpkin > Suggested-by: "Michael S. Tsirkin" > Signed-off-by: Stefano Garzarella Acked-by: Michael S. Tsirkin > --- > net/vmw_vsock/virtio_transport_common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > 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