[RFC PATCH 05/10] tcp: implement recvmsg() RX path for devmem TCP
From: Mina Almasry
Date: Mon Jul 10 2023 - 18:34:33 EST
In tcp_recvmsg_locked(), detect if the skb being received by the user
is a devmem skb. In this case - if the user provided the MSG_SOCK_DEVMEM
flag - pass it to tcp_recvmsg_devmem() for custom handling.
tcp_recvmsg_devmem() copies any data in the skb header to the linear
buffer, and returns a cmsg to the user indicating the number of bytes
returned in the linear buffer.
tcp_recvmsg_devmem() then loops over the unaccessible devmem skb frags,
and returns to the user a cmsg_devmem indicating the location of the
data in the dmabuf device memory. cmsg_devmem contains this information:
1. the offset into the dmabuf where the payload starts. 'frag_offset'.
2. the size of the frag. 'frag_size'.
3. an opaque token 'frag_token' to return to the kernel when the buffer
is to be released.
The pages awaiting freeing are stored in the newly added sk->sk_pagepool,
and each page passed to userspace is get_page()'d. This reference is
dropped once the userspace indicates that it is done reading this page.
All pages are released when the socket is destroyed.
Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
---
include/linux/socket.h | 1 +
include/net/sock.h | 2 +
include/uapi/asm-generic/socket.h | 5 +
include/uapi/linux/uio.h | 6 +
net/core/datagram.c | 3 +
net/ipv4/tcp.c | 186 +++++++++++++++++++++++++++++-
net/ipv4/tcp_ipv4.c | 8 ++
7 files changed, 209 insertions(+), 2 deletions(-)
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 13c3a237b9c9..12905b2f1215 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -326,6 +326,7 @@ struct ucred {
* plain text and require encryption
*/
+#define MSG_SOCK_DEVMEM 0x2000000 /* Receive devmem skbs as cmsg */
#define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
#define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
diff --git a/include/net/sock.h b/include/net/sock.h
index 6f428a7f3567..c615666ff19a 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -353,6 +353,7 @@ struct sk_filter;
* @sk_txtime_unused: unused txtime flags
* @ns_tracker: tracker for netns reference
* @sk_bind2_node: bind node in the bhash2 table
+ * @sk_pagepool: page pool associated with this socket.
*/
struct sock {
/*
@@ -545,6 +546,7 @@ struct sock {
struct rcu_head sk_rcu;
netns_tracker ns_tracker;
struct hlist_node sk_bind2_node;
+ struct xarray sk_pagepool;
};
enum sk_pacing {
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 638230899e98..88f9234f78cb 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -132,6 +132,11 @@
#define SO_RCVMARK 75
+#define SO_DEVMEM_HEADER 98
+#define SCM_DEVMEM_HEADER SO_DEVMEM_HEADER
+#define SO_DEVMEM_OFFSET 99
+#define SCM_DEVMEM_OFFSET SO_DEVMEM_OFFSET
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/include/uapi/linux/uio.h b/include/uapi/linux/uio.h
index 059b1a9147f4..8b0be0f50838 100644
--- a/include/uapi/linux/uio.h
+++ b/include/uapi/linux/uio.h
@@ -20,6 +20,12 @@ struct iovec
__kernel_size_t iov_len; /* Must be size_t (1003.1g) */
};
+struct cmsg_devmem {
+ __u32 frag_offset;
+ __u32 frag_size;
+ __u32 frag_token;
+};
+
/*
* UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)
*/
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 176eb5834746..3a82598aa6ed 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -455,6 +455,9 @@ static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
skb_walk_frags(skb, frag_iter) {
int end;
+ if (frag_iter->devmem)
+ goto short_copy;
+
WARN_ON(start > offset + len);
end = start + frag_iter->len;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 51e8d5872670..a894b8a9dbb0 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -279,6 +279,7 @@
#include <linux/uaccess.h>
#include <asm/ioctls.h>
#include <net/busy_poll.h>
+#include <linux/dma-buf.h>
/* Track pending CMSGs. */
enum {
@@ -460,6 +461,7 @@ void tcp_init_sock(struct sock *sk)
set_bit(SOCK_SUPPORT_ZC, &sk->sk_socket->flags);
sk_sockets_allocated_inc(sk);
+ xa_init_flags(&sk->sk_pagepool, XA_FLAGS_ALLOC);
}
EXPORT_SYMBOL(tcp_init_sock);
@@ -2408,6 +2410,165 @@ static int tcp_inq_hint(struct sock *sk)
return inq;
}
+static int tcp_recvmsg_devmem(const struct sock *sk, const struct sk_buff *skb,
+ unsigned int offset, struct msghdr *msg, int len)
+{
+ unsigned int start = skb_headlen(skb);
+ struct cmsg_devmem cmsg_devmem = { 0 };
+ unsigned int tokens_added_idx = 0;
+ int i, copy = start - offset, n;
+ struct sk_buff *frag_iter;
+ u32 *tokens_added;
+ int err = 0;
+
+ if (!skb->devmem)
+ return -ENODEV;
+
+ tokens_added = kzalloc(sizeof(u32) * skb_shinfo(skb)->nr_frags,
+ GFP_KERNEL);
+
+ if (!tokens_added)
+ return -ENOMEM;
+
+ /* Copy header. */
+ if (copy > 0) {
+ copy = min(copy, len);
+
+ n = copy_to_iter(skb->data + offset, copy, &msg->msg_iter);
+ if (n != copy) {
+ err = -EFAULT;
+ goto err_release_pages;
+ }
+
+ offset += copy;
+ len -= copy;
+
+ /* First a cmsg_devmem for # bytes copied to user buffer */
+ cmsg_devmem.frag_size = copy;
+ err = put_cmsg(msg, SOL_SOCKET, SO_DEVMEM_HEADER,
+ sizeof(cmsg_devmem), &cmsg_devmem);
+ if (err)
+ goto err_release_pages;
+
+ if (len == 0)
+ goto out;
+ }
+
+ /* after that, send information of devmem pages through a sequence
+ * of cmsg
+ */
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ struct page *page = skb_frag_page(frag);
+ struct dma_buf_pages *priv;
+ u32 user_token, frag_offset;
+ struct page *dmabuf_pages;
+ int end;
+
+ /* skb->devmem should indicate that ALL the pages in this skb
+ * are dma buf pages. We're checking for that flag above, but
+ * also check individual pages here. If the driver is not
+ * setting skb->devmem correctly, we still don't want to crash
+ * here when accessing pgmap or priv below.
+ */
+ if (!is_dma_buf_page(page)) {
+ net_err_ratelimited("Found non-devmem skb with dma_buf "
+ "page");
+ err = -ENODEV;
+ goto err_release_pages;
+ }
+
+ end = start + skb_frag_size(frag);
+ copy = end - offset;
+ memset(&cmsg_devmem, 0, sizeof(cmsg_devmem));
+
+ if (copy > 0) {
+ copy = min(copy, len);
+
+ priv = (struct dma_buf_pages *)page->pp->mp_priv;
+
+ dmabuf_pages = priv->pages;
+ frag_offset = ((page - dmabuf_pages) << PAGE_SHIFT) +
+ skb_frag_off(frag) + offset - start;
+ cmsg_devmem.frag_offset = frag_offset;
+ cmsg_devmem.frag_size = copy;
+ err = xa_alloc((struct xarray *)&sk->sk_pagepool,
+ &user_token, page, xa_limit_31b,
+ GFP_KERNEL);
+ if (err)
+ goto err_release_pages;
+
+ tokens_added[tokens_added_idx++] = user_token;
+
+ get_page(page);
+ cmsg_devmem.frag_token = user_token;
+
+ offset += copy;
+ len -= copy;
+
+ err = put_cmsg(msg, SOL_SOCKET, SO_DEVMEM_OFFSET,
+ sizeof(cmsg_devmem), &cmsg_devmem);
+ if (err) {
+ put_page(page);
+ goto err_release_pages;
+ }
+
+ if (len == 0)
+ goto out;
+ }
+ start = end;
+ }
+
+ if (!len)
+ goto out;
+
+ /* if len is not satisfied yet, we need to skb_walk_frags() to satisfy
+ * len
+ */
+ skb_walk_frags(skb, frag_iter)
+ {
+ int end;
+
+ if (!frag_iter->devmem) {
+ err = -EFAULT;
+ goto err_release_pages;
+ }
+
+ WARN_ON(start > offset + len);
+ end = start + frag_iter->len;
+ copy = end - offset;
+ if (copy > 0) {
+ if (copy > len)
+ copy = len;
+ err = tcp_recvmsg_devmem(sk, frag_iter, offset - start,
+ msg, copy);
+ if (err)
+ goto err_release_pages;
+ len -= copy;
+ if (len == 0)
+ goto out;
+ offset += copy;
+ }
+ start = end;
+ }
+
+ if (len) {
+ err = -EFAULT;
+ goto err_release_pages;
+ }
+
+ goto out;
+
+err_release_pages:
+ for (i = 0; i < tokens_added_idx; i++)
+ put_page(xa_erase((struct xarray *)&sk->sk_pagepool,
+ tokens_added[i]));
+
+out:
+ kfree(tokens_added);
+ return err;
+}
+
/*
* This routine copies from a sock struct into the user buffer.
*
@@ -2428,7 +2589,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
int err;
int target; /* Read at least this many bytes */
long timeo;
- struct sk_buff *skb, *last;
+ struct sk_buff *skb, *last, *skb_last_copied = NULL;
u32 urg_hole = 0;
err = -ENOTCONN;
@@ -2593,7 +2754,27 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
}
}
- if (!(flags & MSG_TRUNC)) {
+ if (skb_last_copied && skb_last_copied->devmem != skb->devmem)
+ break;
+
+ if (skb->devmem) {
+ if (!(flags & MSG_SOCK_DEVMEM)) {
+ /* skb->devmem skbs can only be received with
+ * the MSG_SOCK_DEVMEM flag.
+ */
+
+ copied = -EFAULT;
+ break;
+ }
+
+ err = tcp_recvmsg_devmem(sk, skb, offset, msg, used);
+ if (err) {
+ if (!copied)
+ copied = -EFAULT;
+ break;
+ }
+ skb_last_copied = skb;
+ } else if (!(flags & MSG_TRUNC)) {
err = skb_copy_datagram_msg(skb, offset, msg, used);
if (err) {
/* Exception. Bailout! */
@@ -2601,6 +2782,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
copied = -EFAULT;
break;
}
+ skb_last_copied = skb;
}
WRITE_ONCE(*seq, *seq + used);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 06d2573685ca..d7dee38e0410 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2291,6 +2291,14 @@ void tcp_v4_destroy_sock(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
+ unsigned long index;
+ struct page *page;
+
+ xa_for_each(&sk->sk_pagepool, index, page)
+ put_page(page);
+
+ xa_destroy(&sk->sk_pagepool);
+
trace_tcp_destroy_sock(sk);
tcp_clear_xmit_timers(sk);
--
2.41.0.390.g38632f3daf-goog