[PATCH v1 13/15] io_uring/zcrx: add copy fallback

[David Wei <dw@davidwei.uk>]

From: Pavel Begunkov <asml.silence@gmail.com>

There are scenarios in which the zerocopy path might get a normal
in-kernel buffer, it could be a mis-steered packet or simply the linear
part of an skb. Another use case is to allow the driver to allocate
kernel pages when it's out of zc buffers, which makes it more resilient
to spikes in load and allow the user to choose the balance between the
amount of memory provided and performance.

At the moment we fail such requests. Instead, grab a buffer from the
page pool, copy data there, and return back to user in the usual way.
Because the refill ring is private to the napi our page pool is running
from, it's done by stopping the napi via napi_execute() helper. It grabs
only one buffer, which is inefficient, and improving it is left for
follow up patches.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Wei <dw@davidwei.uk>
---
 io_uring/zcrx.c | 125 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 118 insertions(+), 7 deletions(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 8166d8a2656e..d21e7017deb3 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -5,6 +5,8 @@
 #include <linux/nospec.h>
 #include <linux/netdevice.h>
 #include <linux/io_uring.h>
+#include <linux/skbuff_ref.h>
+#include <net/busy_poll.h>
 #include <net/page_pool/helpers.h>
 #include <trace/events/page_pool.h>
 #include <net/tcp.h>
@@ -28,6 +30,11 @@ struct io_zcrx_args {
 	struct socket		*sock;
 };
 
+struct io_zc_refill_data {
+	struct io_zcrx_ifq *ifq;
+	struct net_iov *niov;
+};
+
 static inline struct io_zcrx_area *io_zcrx_iov_to_area(const struct net_iov *niov)
 {
 	struct net_iov_area *owner = net_iov_owner(niov);
@@ -35,6 +42,13 @@ static inline struct io_zcrx_area *io_zcrx_iov_to_area(const struct net_iov *nio
 	return container_of(owner, struct io_zcrx_area, nia);
 }
 
+static inline struct page *io_zcrx_iov_page(const struct net_iov *niov)
+{
+	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
+
+	return area->pages[net_iov_idx(niov)];
+}
+
 static int io_allocate_rbuf_ring(struct io_zcrx_ifq *ifq,
 				 struct io_uring_zcrx_ifq_reg *reg)
 {
@@ -475,6 +489,34 @@ const struct memory_provider_ops io_uring_pp_zc_ops = {
 	.scrub			= io_pp_zc_scrub,
 };
 
+static void io_napi_refill(void *data)
+{
+	struct io_zc_refill_data *rd = data;
+	struct io_zcrx_ifq *ifq = rd->ifq;
+	netmem_ref netmem;
+
+	if (WARN_ON_ONCE(!ifq->pp))
+		return;
+
+	netmem = page_pool_alloc_netmem(ifq->pp, GFP_ATOMIC | __GFP_NOWARN);
+	if (!netmem)
+		return;
+	if (WARN_ON_ONCE(!netmem_is_net_iov(netmem)))
+		return;
+
+	rd->niov = netmem_to_net_iov(netmem);
+}
+
+static struct net_iov *io_zc_get_buf_task_safe(struct io_zcrx_ifq *ifq)
+{
+	struct io_zc_refill_data rd = {
+		.ifq = ifq,
+	};
+
+	napi_execute(ifq->napi_id, io_napi_refill, &rd);
+	return rd.niov;
+}
+
 static bool io_zcrx_queue_cqe(struct io_kiocb *req, struct net_iov *niov,
 			      struct io_zcrx_ifq *ifq, int off, int len)
 {
@@ -498,6 +540,45 @@ static bool io_zcrx_queue_cqe(struct io_kiocb *req, struct net_iov *niov,
 	return true;
 }
 
+static ssize_t io_zcrx_copy_chunk(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
+				  void *data, unsigned int offset, size_t len)
+{
+	size_t copy_size, copied = 0;
+	int ret = 0, off = 0;
+	struct page *page;
+	u8 *vaddr;
+
+	do {
+		struct net_iov *niov;
+
+		niov = io_zc_get_buf_task_safe(ifq);
+		if (!niov) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		page = io_zcrx_iov_page(niov);
+		vaddr = kmap_local_page(page);
+		copy_size = min_t(size_t, PAGE_SIZE, len);
+		memcpy(vaddr, data + offset, copy_size);
+		kunmap_local(vaddr);
+
+		if (!io_zcrx_queue_cqe(req, niov, ifq, off, copy_size)) {
+			napi_pp_put_page(net_iov_to_netmem(niov));
+			return -ENOSPC;
+		}
+
+		io_zcrx_get_buf_uref(niov);
+		napi_pp_put_page(net_iov_to_netmem(niov));
+
+		offset += copy_size;
+		len -= copy_size;
+		copied += copy_size;
+	} while (offset < len);
+
+	return copied ? copied : ret;
+}
+
 static int io_zcrx_recv_frag(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 			     const skb_frag_t *frag, int off, int len)
 {
@@ -505,8 +586,24 @@ static int io_zcrx_recv_frag(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
 
 	off += skb_frag_off(frag);
 
-	if (unlikely(!skb_frag_is_net_iov(frag)))
-		return -EOPNOTSUPP;
+	if (unlikely(!skb_frag_is_net_iov(frag))) {
+		struct page *page = skb_frag_page(frag);
+		u32 p_off, p_len, t, copied = 0;
+		u8 *vaddr;
+		int ret = 0;
+
+		skb_frag_foreach_page(frag, off, len,
+				      page, p_off, p_len, t) {
+			vaddr = kmap_local_page(page);
+			ret = io_zcrx_copy_chunk(req, ifq, vaddr, p_off, p_len);
+			kunmap_local(vaddr);
+
+			if (ret < 0)
+				return copied ? copied : ret;
+			copied += ret;
+		}
+		return copied;
+	}
 
 	niov = netmem_to_net_iov(frag->netmem);
 	if (niov->pp->mp_ops != &io_uring_pp_zc_ops ||
@@ -527,15 +624,29 @@ io_zcrx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
 	struct io_zcrx_ifq *ifq = args->ifq;
 	struct io_kiocb *req = args->req;
 	struct sk_buff *frag_iter;
-	unsigned start, start_off;
+	unsigned start, start_off = offset;
 	int i, copy, end, off;
 	int ret = 0;
 
-	start = skb_headlen(skb);
-	start_off = offset;
+	if (unlikely(offset < skb_headlen(skb))) {
+		ssize_t copied;
+		size_t to_copy;
 
-	if (offset < start)
-		return -EOPNOTSUPP;
+		to_copy = min_t(size_t, skb_headlen(skb) - offset, len);
+		copied = io_zcrx_copy_chunk(req, ifq, skb->data, offset, to_copy);
+		if (copied < 0) {
+			ret = copied;
+			goto out;
+		}
+		offset += copied;
+		len -= copied;
+		if (!len)
+			goto out;
+		if (offset != skb_headlen(skb))
+			goto out;
+	}
+
+	start = skb_headlen(skb);
 
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 		const skb_frag_t *frag;
-- 
2.43.5