macvtap: macvtapTX zero-copy support

Only 128 bytes is copied, the rest of data is DMA mapped directly from
userspace.

Signed-off-by: Shirley Ma <xma@...ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 121 insertions, 11 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index ecee0fe65a97..ab96c319a240 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -60,6 +60,7 @@ static struct proto macvtap_proto = {
  */
 static dev_t macvtap_major;
 #define MACVTAP_NUM_DEVS 65536
+#define GOODCOPY_LEN 128
 static struct class *macvtap_class;
 static struct cdev macvtap_cdev;
 
@@ -340,6 +341,7 @@ static int macvtap_open(struct inode *inode, struct file *file)
 {
         struct net *net = current->nsproxy->net_ns;
         struct net_device *dev = dev_get_by_index(net, iminor(inode));
+        struct macvlan_dev *vlan = netdev_priv(dev);
         struct macvtap_queue *q;
         int err;
 
@@ -369,6 +371,16 @@ static int macvtap_open(struct inode *inode, struct file *file)
         q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP;
         q->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
 
+        /*
+         * so far only KVM virtio_net uses macvtap, enable zero copy between
+         * guest kernel and host kernel when lower device supports zerocopy
+         */
+        if (vlan) {
+                if ((vlan->lowerdev->features & NETIF_F_HIGHDMA) &&
+                    (vlan->lowerdev->features & NETIF_F_SG))
+                        sock_set_flag(&q->sk, SOCK_ZEROCOPY);
+        }
+
         err = macvtap_set_queue(dev, file, q);
         if (err)
                 sock_put(&q->sk);
@@ -433,6 +445,80 @@ static inline struct sk_buff *macvtap_alloc_skb(struct sock *sk, size_t prepad,
         return skb;
 }
 
+/* set skb frags from iovec, this can move to core network code for reuse */
+static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
+                                  int offset, size_t count)
+{
+        int len = iov_length(from, count) - offset;
+        int copy = skb_headlen(skb);
+        int size, offset1 = 0;
+        int i = 0;
+        skb_frag_t *f;
+
+        /* Skip over from offset */
+        while (count && (offset >= from->iov_len)) {
+                offset -= from->iov_len;
+                ++from;
+                --count;
+        }
+
+        /* copy up to skb headlen */
+        while (count && (copy > 0)) {
+                size = min_t(unsigned int, copy, from->iov_len - offset);
+                if (copy_from_user(skb->data + offset1, from->iov_base + offset,
+                                   size))
+                        return -EFAULT;
+                if (copy > size) {
+                        ++from;
+                        --count;
+                }
+                copy -= size;
+                offset1 += size;
+                offset = 0;
+        }
+
+        if (len == offset1)
+                return 0;
+
+        while (count--) {
+                struct page *page[MAX_SKB_FRAGS];
+                int num_pages;
+                unsigned long base;
+
+                len = from->iov_len - offset1;
+                if (!len) {
+                        offset1 = 0;
+                        ++from;
+                        continue;
+                }
+                base = (unsigned long)from->iov_base + offset1;
+                size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
+                num_pages = get_user_pages_fast(base, size, 0, &page[i]);
+                if ((num_pages != size) ||
+                    (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags))
+                        /* put_page is in skb free */
+                        return -EFAULT;
+                skb->data_len += len;
+                skb->len += len;
+                skb->truesize += len;
+                atomic_add(len, &skb->sk->sk_wmem_alloc);
+                while (len) {
+                        f = &skb_shinfo(skb)->frags[i];
+                        f->page = page[i];
+                        f->page_offset = base & ~PAGE_MASK;
+                        f->size = min_t(int, len, PAGE_SIZE - f->page_offset);
+                        skb_shinfo(skb)->nr_frags++;
+                        /* increase sk_wmem_alloc */
+                        base += f->size;
+                        len -= f->size;
+                        i++;
+                }
+                offset1 = 0;
+                ++from;
+        }
+        return 0;
+}
+
 /*
  * macvtap_skb_from_vnet_hdr and macvtap_skb_to_vnet_hdr should
  * be shared with the tun/tap driver.
@@ -517,16 +603,18 @@ static int macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
 
 
 /* Get packet from user space buffer */
-static ssize_t macvtap_get_user(struct macvtap_queue *q,
-                                const struct iovec *iv, size_t count,
-                                int noblock)
+static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
+                                const struct iovec *iv, unsigned long total_len,
+                                size_t count, int noblock)
 {
         struct sk_buff *skb;
         struct macvlan_dev *vlan;
-        size_t len = count;
+        unsigned long len = total_len;
         int err;
         struct virtio_net_hdr vnet_hdr = { 0 };
         int vnet_hdr_len = 0;
+        int copylen;
+        bool zerocopy = false;
 
         if (q->flags & IFF_VNET_HDR) {
                 vnet_hdr_len = q->vnet_hdr_sz;
@@ -554,12 +642,31 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q,
         if (unlikely(len < ETH_HLEN))
                 goto err;
 
-        skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, len, vnet_hdr.hdr_len,
-                                noblock, &err);
+        if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY))
+                zerocopy = true;
+
+        if (zerocopy) {
+                /* There are 256 bytes to be copied in skb, so there is enough
+                 * room for skb expand head in case it is used.
+                 * The rest buffer is mapped from userspace.
+                 */
+                copylen = vnet_hdr.hdr_len;
+                if (!copylen)
+                        copylen = GOODCOPY_LEN;
+        } else
+                copylen = len;
+
+        skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
+                                vnet_hdr.hdr_len, noblock, &err);
         if (!skb)
                 goto err;
 
-        err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len, len);
+        if (zerocopy) {
+                err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count);
+                skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+        } else
+                err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len,
+                                                   len);
         if (err)
                 goto err_kfree;
 
@@ -575,13 +682,16 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q,
 
         rcu_read_lock_bh();
         vlan = rcu_dereference_bh(q->vlan);
+        /* copy skb_ubuf_info for callback when skb has no error */
+        if (zerocopy)
+                skb_shinfo(skb)->destructor_arg = m->msg_control;
         if (vlan)
                 macvlan_start_xmit(skb, vlan->dev);
         else
                 kfree_skb(skb);
         rcu_read_unlock_bh();
 
-        return count;
+        return total_len;
 
 err_kfree:
         kfree_skb(skb);
@@ -603,8 +713,8 @@ static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
         ssize_t result = -ENOLINK;
         struct macvtap_queue *q = file->private_data;
 
-        result = macvtap_get_user(q, iv, iov_length(iv, count),
-                              file->f_flags & O_NONBLOCK);
+        result = macvtap_get_user(q, NULL, iv, iov_length(iv, count), count,
+                                  file->f_flags & O_NONBLOCK);
         return result;
 }
 
@@ -817,7 +927,7 @@ static int macvtap_sendmsg(struct kiocb *iocb, struct socket *sock,
                            struct msghdr *m, size_t total_len)
 {
         struct macvtap_queue *q = container_of(sock, struct macvtap_queue, sock);
-        return macvtap_get_user(q, m->msg_iov, total_len,
+        return macvtap_get_user(q, m, m->msg_iov, total_len, m->msg_iovlen,
                             m->msg_flags & MSG_DONTWAIT);
 }