vhost: don't bother copying iovecs in handle_rx(), kill memcpy_toiovecend()

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 23 insertions, 88 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d86cc9bb9ea4..e022cc40303d 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -84,10 +84,6 @@ struct vhost_net_ubuf_ref {
 
 struct vhost_net_virtqueue {
         struct vhost_virtqueue vq;
-        /* hdr is used to store the virtio header.
-         * Since each iovec has >= 1 byte length, we never need more than
-         * header length entries to store the header. */
-        struct iovec hdr[sizeof(struct virtio_net_hdr_mrg_rxbuf)];
         size_t vhost_hlen;
         size_t sock_hlen;
         /* vhost zerocopy support fields below: */
@@ -235,44 +231,6 @@ static bool vhost_sock_zcopy(struct socket *sock)
                 sock_flag(sock->sk, SOCK_ZEROCOPY);
 }
 
-/* Pop first len bytes from iovec. Return number of segments used. */
-static int move_iovec_hdr(struct iovec *from, struct iovec *to,
-                          size_t len, int iov_count)
-{
-        int seg = 0;
-        size_t size;
-
-        while (len && seg < iov_count) {
-                size = min(from->iov_len, len);
-                to->iov_base = from->iov_base;
-                to->iov_len = size;
-                from->iov_len -= size;
-                from->iov_base += size;
-                len -= size;
-                ++from;
-                ++to;
-                ++seg;
-        }
-        return seg;
-}
-/* Copy iovec entries for len bytes from iovec. */
-static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
-                           size_t len, int iovcount)
-{
-        int seg = 0;
-        size_t size;
-
-        while (len && seg < iovcount) {
-                size = min(from->iov_len, len);
-                to->iov_base = from->iov_base;
-                to->iov_len = size;
-                len -= size;
-                ++from;
-                ++to;
-                ++seg;
-        }
-}
-
 /* In case of DMA done not in order in lower device driver for some reason.
  * upend_idx is used to track end of used idx, done_idx is used to track head
  * of used idx. Once lower device DMA done contiguously, we will signal KVM
@@ -570,9 +528,9 @@ static void handle_rx(struct vhost_net *net)
                 .msg_controllen = 0,
                 .msg_flags = MSG_DONTWAIT,
         };
-        struct virtio_net_hdr_mrg_rxbuf hdr = {
-                .hdr.flags = 0,
-                .hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
+        struct virtio_net_hdr hdr = {
+                .flags = 0,
+                .gso_type = VIRTIO_NET_HDR_GSO_NONE
         };
         size_t total_len = 0;
         int err, mergeable;
@@ -580,6 +538,7 @@ static void handle_rx(struct vhost_net *net)
         size_t vhost_hlen, sock_hlen;
         size_t vhost_len, sock_len;
         struct socket *sock;
+        struct iov_iter fixup;
 
         mutex_lock(&vq->mutex);
         sock = vq->private_data;
@@ -624,14 +583,19 @@ static void handle_rx(struct vhost_net *net)
                         break;
                 }
                 /* We don't need to be notified again. */
-                if (unlikely((vhost_hlen)))
-                        /* Skip header. TODO: support TSO. */
-                        move_iovec_hdr(vq->iov, nvq->hdr, vhost_hlen, in);
-                else
-                        /* Copy the header for use in VIRTIO_NET_F_MRG_RXBUF:
-                         * needed because recvmsg can modify msg_iov. */
-                        copy_iovec_hdr(vq->iov, nvq->hdr, sock_hlen, in);
-                iov_iter_init(&msg.msg_iter, READ, vq->iov, in, sock_len);
+                iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
+                fixup = msg.msg_iter;
+                if (unlikely((vhost_hlen))) {
+                        /* We will supply the header ourselves
+                         * TODO: support TSO.
+                         */
+                        iov_iter_advance(&msg.msg_iter, vhost_hlen);
+                } else {
+                        /* It'll come from socket; we'll need to patch
+                         * ->num_buffers over if VIRTIO_NET_F_MRG_RXBUF
+                         */
+                        iov_iter_advance(&fixup, sizeof(hdr));
+                }
                 err = sock->ops->recvmsg(NULL, sock, &msg,
                                          sock_len, MSG_DONTWAIT | MSG_TRUNC);
                 /* Userspace might have consumed the packet meanwhile:
@@ -643,18 +607,18 @@ static void handle_rx(struct vhost_net *net)
                         vhost_discard_vq_desc(vq, headcount);
                         continue;
                 }
+                /* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
                 if (unlikely(vhost_hlen) &&
-                    memcpy_toiovecend(nvq->hdr, (unsigned char *)&hdr, 0,
-                                      vhost_hlen)) {
+                    copy_to_iter(&hdr, sizeof(hdr), &fixup) != sizeof(hdr)) {
                         vq_err(vq, "Unable to write vnet_hdr at addr %p\n",
                                vq->iov->iov_base);
                         break;
                 }
-                /* TODO: Should check and handle checksum. */
+                /* Supply (or replace) ->num_buffers if VIRTIO_NET_F_MRG_RXBUF
+                 * TODO: Should check and handle checksum.
+                 */
                 if (likely(mergeable) &&
-                    memcpy_toiovecend(nvq->hdr, (unsigned char *)&headcount,
-                                      offsetof(typeof(hdr), num_buffers),
-                                      sizeof hdr.num_buffers)) {
+                    copy_to_iter(&headcount, 2, &fixup) != 2) {
                         vq_err(vq, "Failed num_buffers write");
                         vhost_discard_vq_desc(vq, headcount);
                         break;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index af3439f4ebf2..02bd8a92038a 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -137,7 +137,4 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, struct io
 
 int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
                         int offset, int len);
-int memcpy_toiovecend(const struct iovec *v, unsigned char *kdata,
-                      int offset, int len);
-
 #endif
diff --git a/lib/iovec.c b/lib/iovec.c
index 4a90875c64ae..d8f17a9b1ccf 100644
--- a/lib/iovec.c
+++ b/lib/iovec.c
@@ -3,32 +3,6 @@
 #include <linux/uio.h>
 
 /*
- *      Copy kernel to iovec. Returns -EFAULT on error.
- */
-
-int memcpy_toiovecend(const struct iovec *iov, unsigned char *kdata,
-                      int offset, int len)
-{
-        int copy;
-        for (; len > 0; ++iov) {
-                /* Skip over the finished iovecs */
-                if (unlikely(offset >= iov->iov_len)) {
-                        offset -= iov->iov_len;
-                        continue;
-                }
-                copy = min_t(unsigned int, iov->iov_len - offset, len);
-                if (copy_to_user(iov->iov_base + offset, kdata, copy))
-                        return -EFAULT;
-                offset = 0;
-                kdata += copy;
-                len -= copy;
-        }
-
-        return 0;
-}
-EXPORT_SYMBOL(memcpy_toiovecend);
-
-/*
  *      Copy iovec to kernel. Returns -EFAULT on error.
  */