Re: [PATCH V2 net-next 2/2] vhost-net: reduce one userspace copy when building XDP buff
From: Jakub Kicinski <kuba@kernel.org>
Date: 2025-06-28 00:48:26
Also in:
kvm, lkml, virtualization
On Thu, 26 Jun 2025 10:14:45 +0800 Jason Wang wrote:
quoted hunk ↗ jump to hunk
--- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c@@ -690,13 +690,13 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, if (unlikely(!buf)) return -ENOMEM; - copied = copy_from_iter(buf, sock_hlen, from); - if (copied != sock_hlen) { + copied = copy_from_iter(buf + pad - sock_hlen, len, from); + if (copied != len) { ret = -EFAULT; goto err; } - gso = buf; + gso = buf + pad - sock_hlen; if (!sock_hlen) memset(buf, 0, pad);@@ -715,12 +715,8 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, } } - len -= sock_hlen;
we used to adjust @len here, now we don't..
- copied = copy_from_iter(buf + pad, len, from);
- if (copied != len) {
- ret = -EFAULT;
- goto err;
- }
+ /* pad contains sock_hlen */
+ memcpy(buf, buf + pad - sock_hlen, sock_hlen);
xdp_init_buff(xdp, buflen, NULL);
xdp_prepare_buff(xdp, buf, pad, len, true);.. yet we still use len as the packet size here. -- pw-bot: cr