[PATCH net-next v26 09/13] tcp: RX path for devmem TCP

From: Mina Almasry
Date: Tue Sep 10 2024 - 13:20:05 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_user_frags, 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: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: Kaiyuan Zhang <kaiyuanz@xxxxxxxxxx>
Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>

---

v20:
- Change `offset = 0` to `offset = offset - start` to resolve issue
reported by Taehee.

v16:
- Fix number assignement (Arnd).

v13:
- Refactored user frags cleanup into a common function to avoid
__maybe_unused. (Pavel)
- change to offset = 0 for some improved clarity.

v11:
- Refactor to common function te remove conditional lock sparse warning
(Paolo)

v7:
- Updated the SO_DEVMEM_* uapi to use the next available entries (Arnd).
- Updated dmabuf_cmsg struct to be __u64 padded (Arnd).
- Squashed fix from Eric to initialize sk_user_frags for passive
sockets (Eric).

v6
- skb->dmabuf -> skb->readable (Pavel)
- Fixed asm definitions of SO_DEVMEM_LINEAR/SO_DEVMEM_DMABUF not found
on some archs.
- Squashed in locking optimizations from edumazet@xxxxxxxxxx. With this
change we lock the xarray once per per tcp_recvmsg_dmabuf() rather
than once per frag in xa_alloc().

Changes in v1:
- Added dmabuf_id to dmabuf_cmsg (David/Stan).
- Devmem -> dmabuf (David).
- Change tcp_recvmsg_dmabuf() check to skb->dmabuf (Paolo).
- Use __skb_frag_ref() & napi_pp_put_page() for refcounting (Yunsheng).

RFC v3:
- Fixed issue with put_cmsg() failing silently.

---
arch/alpha/include/uapi/asm/socket.h | 5 +
arch/mips/include/uapi/asm/socket.h | 5 +
arch/parisc/include/uapi/asm/socket.h | 5 +
arch/sparc/include/uapi/asm/socket.h | 5 +
include/linux/socket.h | 1 +
include/net/sock.h | 2 +
include/uapi/asm-generic/socket.h | 5 +
include/uapi/linux/uio.h | 13 ++
net/core/devmem.h | 22 +++
net/ipv4/tcp.c | 257 +++++++++++++++++++++++++-
net/ipv4/tcp_ipv4.c | 16 ++
net/ipv4/tcp_minisocks.c | 2 +
12 files changed, 333 insertions(+), 5 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index e94f621903fe..ef4656a41058 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -140,6 +140,11 @@
#define SO_PASSPIDFD 76
#define SO_PEERPIDFD 77

+#define SO_DEVMEM_LINEAR 78
+#define SCM_DEVMEM_LINEAR SO_DEVMEM_LINEAR
+#define SO_DEVMEM_DMABUF 79
+#define SCM_DEVMEM_DMABUF SO_DEVMEM_DMABUF
+
#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 60ebaed28a4c..414807d55e33 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -151,6 +151,11 @@
#define SO_PASSPIDFD 76
#define SO_PEERPIDFD 77

+#define SO_DEVMEM_LINEAR 78
+#define SCM_DEVMEM_LINEAR SO_DEVMEM_LINEAR
+#define SO_DEVMEM_DMABUF 79
+#define SCM_DEVMEM_DMABUF SO_DEVMEM_DMABUF
+
#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index be264c2b1a11..2b817efd4544 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -132,6 +132,11 @@
#define SO_PASSPIDFD 0x404A
#define SO_PEERPIDFD 0x404B

+#define SO_DEVMEM_LINEAR 78
+#define SCM_DEVMEM_LINEAR SO_DEVMEM_LINEAR
+#define SO_DEVMEM_DMABUF 79
+#define SCM_DEVMEM_DMABUF SO_DEVMEM_DMABUF
+
#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 682da3714686..00248fc68977 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -133,6 +133,11 @@
#define SO_PASSPIDFD 0x0055
#define SO_PEERPIDFD 0x0056

+#define SO_DEVMEM_LINEAR 0x0057
+#define SCM_DEVMEM_LINEAR SO_DEVMEM_LINEAR
+#define SO_DEVMEM_DMABUF 0x0058
+#define SCM_DEVMEM_DMABUF SO_DEVMEM_DMABUF
+
#if !defined(__KERNEL__)


diff --git a/include/linux/socket.h b/include/linux/socket.h
index df9cdb8bbfb8..d18cc47e89bd 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -327,6 +327,7 @@ 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_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
diff --git a/include/net/sock.h b/include/net/sock.h
index f51d61fab059..c58ca8dd561b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -337,6 +337,7 @@ struct sk_filter;
* @sk_txtime_report_errors: set report errors mode for SO_TXTIME
* @sk_txtime_unused: unused txtime flags
* @ns_tracker: tracker for netns reference
+ * @sk_user_frags: xarray of pages the user is holding a reference on.
*/
struct sock {
/*
@@ -542,6 +543,7 @@ struct sock {
#endif
struct rcu_head sk_rcu;
netns_tracker ns_tracker;
+ struct xarray sk_user_frags;
};

struct sock_bh_locked {
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 8ce8a39a1e5f..e993edc9c0ee 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -135,6 +135,11 @@
#define SO_PASSPIDFD 76
#define SO_PEERPIDFD 77

+#define SO_DEVMEM_LINEAR 78
+#define SCM_DEVMEM_LINEAR SO_DEVMEM_LINEAR
+#define SO_DEVMEM_DMABUF 79
+#define SCM_DEVMEM_DMABUF SO_DEVMEM_DMABUF
+
#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..3a22ddae376a 100644
--- a/include/uapi/linux/uio.h
+++ b/include/uapi/linux/uio.h
@@ -20,6 +20,19 @@ struct iovec
__kernel_size_t iov_len; /* Must be size_t (1003.1g) */
};

+struct dmabuf_cmsg {
+ __u64 frag_offset; /* offset into the dmabuf where the frag starts.
+ */
+ __u32 frag_size; /* size of the frag. */
+ __u32 frag_token; /* token representing this frag for
+ * DEVMEM_DONTNEED.
+ */
+ __u32 dmabuf_id; /* dmabuf id this frag belongs to. */
+ __u32 flags; /* Currently unused. Reserved for future
+ * uses.
+ */
+};
+
/*
* UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)
*/
diff --git a/net/core/devmem.h b/net/core/devmem.h
index b1db4877cff9..76099ef9c482 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -91,6 +91,19 @@ net_iov_binding(const struct net_iov *niov)
return net_iov_owner(niov)->binding;
}

+static inline unsigned long net_iov_virtual_addr(const struct net_iov *niov)
+{
+ struct dmabuf_genpool_chunk_owner *owner = net_iov_owner(niov);
+
+ return owner->base_virtual +
+ ((unsigned long)net_iov_idx(niov) << PAGE_SHIFT);
+}
+
+static inline u32 net_iov_binding_id(const struct net_iov *niov)
+{
+ return net_iov_owner(niov)->binding->id;
+}
+
static inline void
net_devmem_dmabuf_binding_get(struct net_devmem_dmabuf_binding *binding)
{
@@ -153,6 +166,15 @@ static inline void net_devmem_free_dmabuf(struct net_iov *ppiov)
{
}

+static inline unsigned long net_iov_virtual_addr(const struct net_iov *niov)
+{
+ return 0;
+}
+
+static inline u32 net_iov_binding_id(const struct net_iov *niov)
+{
+ return 0;
+}
#endif

#endif /* _NET_DEVMEM_H */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 30238963fe99..445d17bd74e5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -285,6 +285,8 @@
#include <trace/events/tcp.h>
#include <net/rps.h>

+#include "../core/devmem.h"
+
/* Track pending CMSGs. */
enum {
TCP_CMSG_INQ = 1,
@@ -471,6 +473,7 @@ 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_user_frags, XA_FLAGS_ALLOC1);
}
EXPORT_SYMBOL(tcp_init_sock);

@@ -2323,6 +2326,220 @@ static int tcp_inq_hint(struct sock *sk)
return inq;
}

+/* batch __xa_alloc() calls and reduce xa_lock()/xa_unlock() overhead. */
+struct tcp_xa_pool {
+ u8 max; /* max <= MAX_SKB_FRAGS */
+ u8 idx; /* idx <= max */
+ __u32 tokens[MAX_SKB_FRAGS];
+ netmem_ref netmems[MAX_SKB_FRAGS];
+};
+
+static void tcp_xa_pool_commit_locked(struct sock *sk, struct tcp_xa_pool *p)
+{
+ int i;
+
+ /* Commit part that has been copied to user space. */
+ for (i = 0; i < p->idx; i++)
+ __xa_cmpxchg(&sk->sk_user_frags, p->tokens[i], XA_ZERO_ENTRY,
+ (__force void *)p->netmems[i], GFP_KERNEL);
+ /* Rollback what has been pre-allocated and is no longer needed. */
+ for (; i < p->max; i++)
+ __xa_erase(&sk->sk_user_frags, p->tokens[i]);
+
+ p->max = 0;
+ p->idx = 0;
+}
+
+static void tcp_xa_pool_commit(struct sock *sk, struct tcp_xa_pool *p)
+{
+ if (!p->max)
+ return;
+
+ xa_lock_bh(&sk->sk_user_frags);
+
+ tcp_xa_pool_commit_locked(sk, p);
+
+ xa_unlock_bh(&sk->sk_user_frags);
+}
+
+static int tcp_xa_pool_refill(struct sock *sk, struct tcp_xa_pool *p,
+ unsigned int max_frags)
+{
+ int err, k;
+
+ if (p->idx < p->max)
+ return 0;
+
+ xa_lock_bh(&sk->sk_user_frags);
+
+ tcp_xa_pool_commit_locked(sk, p);
+
+ for (k = 0; k < max_frags; k++) {
+ err = __xa_alloc(&sk->sk_user_frags, &p->tokens[k],
+ XA_ZERO_ENTRY, xa_limit_31b, GFP_KERNEL);
+ if (err)
+ break;
+ }
+
+ xa_unlock_bh(&sk->sk_user_frags);
+
+ p->max = k;
+ p->idx = 0;
+ return k ? 0 : err;
+}
+
+/* On error, returns the -errno. On success, returns number of bytes sent to the
+ * user. May not consume all of @remaining_len.
+ */
+static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,
+ unsigned int offset, struct msghdr *msg,
+ int remaining_len)
+{
+ struct dmabuf_cmsg dmabuf_cmsg = { 0 };
+ struct tcp_xa_pool tcp_xa_pool;
+ unsigned int start;
+ int i, copy, n;
+ int sent = 0;
+ int err = 0;
+
+ tcp_xa_pool.max = 0;
+ tcp_xa_pool.idx = 0;
+ do {
+ start = skb_headlen(skb);
+
+ if (skb_frags_readable(skb)) {
+ err = -ENODEV;
+ goto out;
+ }
+
+ /* Copy header. */
+ copy = start - offset;
+ if (copy > 0) {
+ copy = min(copy, remaining_len);
+
+ n = copy_to_iter(skb->data + offset, copy,
+ &msg->msg_iter);
+ if (n != copy) {
+ err = -EFAULT;
+ goto out;
+ }
+
+ offset += copy;
+ remaining_len -= copy;
+
+ /* First a dmabuf_cmsg for # bytes copied to user
+ * buffer.
+ */
+ memset(&dmabuf_cmsg, 0, sizeof(dmabuf_cmsg));
+ dmabuf_cmsg.frag_size = copy;
+ err = put_cmsg(msg, SOL_SOCKET, SO_DEVMEM_LINEAR,
+ sizeof(dmabuf_cmsg), &dmabuf_cmsg);
+ if (err || msg->msg_flags & MSG_CTRUNC) {
+ msg->msg_flags &= ~MSG_CTRUNC;
+ if (!err)
+ err = -ETOOSMALL;
+ goto out;
+ }
+
+ sent += copy;
+
+ if (remaining_len == 0)
+ goto out;
+ }
+
+ /* after that, send information of dmabuf pages through a
+ * sequence of cmsg
+ */
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ struct net_iov *niov;
+ u64 frag_offset;
+ int end;
+
+ /* !skb_frags_readable() should indicate that ALL the
+ * frags in this skb are dmabuf net_iovs. We're checking
+ * for that flag above, but also check individual frags
+ * here. If the tcp stack is not setting
+ * skb_frags_readable() correctly, we still don't want
+ * to crash here.
+ */
+ if (!skb_frag_net_iov(frag)) {
+ net_err_ratelimited("Found non-dmabuf skb with net_iov");
+ err = -ENODEV;
+ goto out;
+ }
+
+ niov = skb_frag_net_iov(frag);
+ end = start + skb_frag_size(frag);
+ copy = end - offset;
+
+ if (copy > 0) {
+ copy = min(copy, remaining_len);
+
+ frag_offset = net_iov_virtual_addr(niov) +
+ skb_frag_off(frag) + offset -
+ start;
+ dmabuf_cmsg.frag_offset = frag_offset;
+ dmabuf_cmsg.frag_size = copy;
+ err = tcp_xa_pool_refill(sk, &tcp_xa_pool,
+ skb_shinfo(skb)->nr_frags - i);
+ if (err)
+ goto out;
+
+ /* Will perform the exchange later */
+ dmabuf_cmsg.frag_token = tcp_xa_pool.tokens[tcp_xa_pool.idx];
+ dmabuf_cmsg.dmabuf_id = net_iov_binding_id(niov);
+
+ offset += copy;
+ remaining_len -= copy;
+
+ err = put_cmsg(msg, SOL_SOCKET,
+ SO_DEVMEM_DMABUF,
+ sizeof(dmabuf_cmsg),
+ &dmabuf_cmsg);
+ if (err || msg->msg_flags & MSG_CTRUNC) {
+ msg->msg_flags &= ~MSG_CTRUNC;
+ if (!err)
+ err = -ETOOSMALL;
+ goto out;
+ }
+
+ atomic_long_inc(&niov->pp_ref_count);
+ tcp_xa_pool.netmems[tcp_xa_pool.idx++] = skb_frag_netmem(frag);
+
+ sent += copy;
+
+ if (remaining_len == 0)
+ goto out;
+ }
+ start = end;
+ }
+
+ tcp_xa_pool_commit(sk, &tcp_xa_pool);
+ if (!remaining_len)
+ goto out;
+
+ /* if remaining_len is not satisfied yet, we need to go to the
+ * next frag in the frag_list to satisfy remaining_len.
+ */
+ skb = skb_shinfo(skb)->frag_list ?: skb->next;
+
+ offset = offset - start;
+ } while (skb);
+
+ if (remaining_len) {
+ err = -EFAULT;
+ goto out;
+ }
+
+out:
+ tcp_xa_pool_commit(sk, &tcp_xa_pool);
+ if (!sent)
+ sent = err;
+
+ return sent;
+}
+
/*
* This routine copies from a sock struct into the user buffer.
*
@@ -2336,6 +2553,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
int *cmsg_flags)
{
struct tcp_sock *tp = tcp_sk(sk);
+ int last_copied_dmabuf = -1; /* uninitialized */
int copied = 0;
u32 peek_seq;
u32 *seq;
@@ -2515,15 +2733,44 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
}

if (!(flags & MSG_TRUNC)) {
- err = skb_copy_datagram_msg(skb, offset, msg, used);
- if (err) {
- /* Exception. Bailout! */
- if (!copied)
- copied = -EFAULT;
+ if (last_copied_dmabuf != -1 &&
+ last_copied_dmabuf != !skb_frags_readable(skb))
break;
+
+ if (skb_frags_readable(skb)) {
+ err = skb_copy_datagram_msg(skb, offset, msg,
+ used);
+ if (err) {
+ /* Exception. Bailout! */
+ if (!copied)
+ copied = -EFAULT;
+ break;
+ }
+ } else {
+ if (!(flags & MSG_SOCK_DEVMEM)) {
+ /* dmabuf skbs can only be received
+ * with the MSG_SOCK_DEVMEM flag.
+ */
+ if (!copied)
+ copied = -EFAULT;
+
+ break;
+ }
+
+ err = tcp_recvmsg_dmabuf(sk, skb, offset, msg,
+ used);
+ if (err <= 0) {
+ if (!copied)
+ copied = -EFAULT;
+
+ break;
+ }
+ used = err;
}
}

+ last_copied_dmabuf = !skb_frags_readable(skb);
+
WRITE_ONCE(*seq, *seq + used);
copied += used;
len -= used;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index eb631e66ee03..5afe5e57c89b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -79,6 +79,7 @@
#include <linux/seq_file.h>
#include <linux/inetdevice.h>
#include <linux/btf_ids.h>
+#include <linux/skbuff_ref.h>

#include <crypto/hash.h>
#include <linux/scatterlist.h>
@@ -2512,10 +2513,25 @@ static void tcp_md5sig_info_free_rcu(struct rcu_head *head)
}
#endif

+static void tcp_release_user_frags(struct sock *sk)
+{
+#ifdef CONFIG_PAGE_POOL
+ unsigned long index;
+ void *netmem;
+
+ xa_for_each(&sk->sk_user_frags, index, netmem)
+ WARN_ON_ONCE(!napi_pp_put_page((__force netmem_ref)netmem));
+#endif
+}
+
void tcp_v4_destroy_sock(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);

+ tcp_release_user_frags(sk);
+
+ xa_destroy(&sk->sk_user_frags);
+
trace_tcp_destroy_sock(sk);

tcp_clear_xmit_timers(sk);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index ad562272db2e..bb1fe1ba867a 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -628,6 +628,8 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,

__TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);

+ xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1);
+
return newsk;
}
EXPORT_SYMBOL(tcp_create_openreq_child);
--
2.46.0.598.g6f2099f65c-goog