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tcp: RX path for devmem TCP

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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@google.com>
Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240910171458.219195-10-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Mina Almasry 2024-09-10 17:14:53 +00:00 committed by Jakub Kicinski
parent 65249feb6b
commit 8f0b3cc9a4
12 changed files with 333 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/alpha/include/uapi/asm/socket.h
View File

@ -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

5
arch/mips/include/uapi/asm/socket.h
View File

@ -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

5
arch/parisc/include/uapi/asm/socket.h
View File

@ -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

5
arch/sparc/include/uapi/asm/socket.h
View File

@ -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__)

1
include/linux/socket.h
View File

@ -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 */

2
include/net/sock.h
View File

@ -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 {

5
include/uapi/asm-generic/socket.h
View File

@ -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__))

13
include/uapi/linux/uio.h
View File

@ -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)
*/

22
net/core/devmem.h
View File

@ -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 */

257
net/ipv4/tcp.c
View File

@ -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);
@ -2328,6 +2331,220 @@ 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.
*
@ -2341,6 +2558,7 @@ 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;
@ -2520,15 +2738,44 @@ 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;

16
net/ipv4/tcp_ipv4.c
View File

@ -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);

2
net/ipv4/tcp_minisocks.c
View File

@ -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);