[PATCH net-next v10 15/22] io_uring/zcrx: implement zerocopy receive pp memory provider

[David Wei <dw@davidwei.uk>]

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

Implement a page pool memory provider for io_uring to receieve in a
zero copy fashion. For that, the provider allocates user pages wrapped
around into struct net_iovs, that are stored in a previously registered
struct net_iov_area.

Unlike the traditional receive, that frees pages and returns them back
to the page pool right after data was copied to the user, e.g. inside
recv(2), we extend the lifetime until the user space confirms that it's
done processing the data. That's done by taking a net_iov reference.
When the user is done with the buffer, it must return it back to the
kernel by posting an entry into the refill ring, which is usually polled
off the io_uring memory provider callback in the page pool's netmem
allocation path.

There is also a separate set of per net_iov "user" references accounting
whether a buffer is currently given to the user (including possible
fragmentation).

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Wei <dw@davidwei.uk>
---
 io_uring/zcrx.c | 263 ++++++++++++++++++++++++++++++++++++++++++++++++
 io_uring/zcrx.h |   3 +
 2 files changed, 266 insertions(+)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index e6cca6747148..64e86d14acc7 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -2,10 +2,17 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/mm.h>
+#include <linux/nospec.h>
 #include <linux/io_uring.h>
 #include <linux/netdevice.h>
 #include <linux/rtnetlink.h>
 
+#include <net/page_pool/helpers.h>
+#include <net/page_pool/memory_provider.h>
+#include <net/netlink.h>
+
+#include <trace/events/page_pool.h>
+
 #include <uapi/linux/io_uring.h>
 
 #include "io_uring.h"
@@ -16,6 +23,33 @@
 
 #define IO_RQ_MAX_ENTRIES		32768
 
+__maybe_unused
+static const struct memory_provider_ops io_uring_pp_zc_ops;
+
+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);
+
+	return container_of(owner, struct io_zcrx_area, nia);
+}
+
+static inline atomic_t *io_get_user_counter(struct net_iov *niov)
+{
+	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
+
+	return &area->user_refs[net_iov_idx(niov)];
+}
+
+static bool io_zcrx_put_niov_uref(struct net_iov *niov)
+{
+	atomic_t *uref = io_get_user_counter(niov);
+
+	if (unlikely(!atomic_read(uref)))
+		return false;
+	atomic_dec(uref);
+	return true;
+}
+
 static int io_allocate_rbuf_ring(struct io_zcrx_ifq *ifq,
 				 struct io_uring_zcrx_ifq_reg *reg,
 				 struct io_uring_region_desc *rd)
@@ -51,6 +85,7 @@ static void io_zcrx_free_area(struct io_zcrx_area *area)
 {
 	kvfree(area->freelist);
 	kvfree(area->nia.niovs);
+	kvfree(area->user_refs);
 	if (area->pages) {
 		unpin_user_pages(area->pages, area->nia.num_niovs);
 		kvfree(area->pages);
@@ -106,6 +141,19 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
 	for (i = 0; i < nr_pages; i++)
 		area->freelist[i] = i;
 
+	area->user_refs = kvmalloc_array(nr_pages, sizeof(area->user_refs[0]),
+					GFP_KERNEL | __GFP_ZERO);
+	if (!area->user_refs)
+		goto err;
+
+	for (i = 0; i < nr_pages; i++) {
+		struct net_iov *niov = &area->nia.niovs[i];
+
+		niov->owner = &area->nia;
+		area->freelist[i] = i;
+		atomic_set(&area->user_refs[i], 0);
+	}
+
 	area->free_count = nr_pages;
 	area->ifq = ifq;
 	/* we're only supporting one area per ifq for now */
@@ -130,6 +178,7 @@ static struct io_zcrx_ifq *io_zcrx_ifq_alloc(struct io_ring_ctx *ctx)
 
 	ifq->if_rxq = -1;
 	ifq->ctx = ctx;
+	spin_lock_init(&ifq->rq_lock);
 	return ifq;
 }
 
@@ -238,7 +287,221 @@ void io_unregister_zcrx_ifqs(struct io_ring_ctx *ctx)
 	io_zcrx_ifq_free(ifq);
 }
 
+static struct net_iov *__io_zcrx_get_free_niov(struct io_zcrx_area *area)
+{
+	unsigned niov_idx;
+
+	lockdep_assert_held(&area->freelist_lock);
+
+	niov_idx = area->freelist[--area->free_count];
+	return &area->nia.niovs[niov_idx];
+}
+
+static void io_zcrx_return_niov_freelist(struct net_iov *niov)
+{
+	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
+
+	spin_lock_bh(&area->freelist_lock);
+	area->freelist[area->free_count++] = net_iov_idx(niov);
+	spin_unlock_bh(&area->freelist_lock);
+}
+
+static void io_zcrx_return_niov(struct net_iov *niov)
+{
+	netmem_ref netmem = net_iov_to_netmem(niov);
+
+	page_pool_put_unrefed_netmem(niov->pp, netmem, -1, false);
+}
+
+static void io_zcrx_scrub(struct io_zcrx_ifq *ifq)
+{
+	struct io_zcrx_area *area = ifq->area;
+	int i;
+
+	if (!area)
+		return;
+
+	/* Reclaim back all buffers given to the user space. */
+	for (i = 0; i < area->nia.num_niovs; i++) {
+		struct net_iov *niov = &area->nia.niovs[i];
+		int nr;
+
+		if (!atomic_read(io_get_user_counter(niov)))
+			continue;
+		nr = atomic_xchg(io_get_user_counter(niov), 0);
+		if (nr && !page_pool_unref_netmem(net_iov_to_netmem(niov), nr))
+			io_zcrx_return_niov(niov);
+	}
+}
+
 void io_shutdown_zcrx_ifqs(struct io_ring_ctx *ctx)
 {
 	lockdep_assert_held(&ctx->uring_lock);
+
+	if (ctx->ifq)
+		io_zcrx_scrub(ctx->ifq);
+}
+
+static inline u32 io_zcrx_rqring_entries(struct io_zcrx_ifq *ifq)
+{
+	u32 entries;
+
+	entries = smp_load_acquire(&ifq->rq_ring->tail) - ifq->cached_rq_head;
+	return min(entries, ifq->rq_entries);
+}
+
+static struct io_uring_zcrx_rqe *io_zcrx_get_rqe(struct io_zcrx_ifq *ifq,
+						 unsigned mask)
+{
+	unsigned int idx = ifq->cached_rq_head++ & mask;
+
+	return &ifq->rqes[idx];
 }
+
+static void io_zcrx_ring_refill(struct page_pool *pp,
+				struct io_zcrx_ifq *ifq)
+{
+	unsigned int mask = ifq->rq_entries - 1;
+	unsigned int entries;
+	netmem_ref netmem;
+
+	spin_lock_bh(&ifq->rq_lock);
+
+	entries = io_zcrx_rqring_entries(ifq);
+	entries = min_t(unsigned, entries, PP_ALLOC_CACHE_REFILL - pp->alloc.count);
+	if (unlikely(!entries)) {
+		spin_unlock_bh(&ifq->rq_lock);
+		return;
+	}
+
+	do {
+		struct io_uring_zcrx_rqe *rqe = io_zcrx_get_rqe(ifq, mask);
+		struct io_zcrx_area *area;
+		struct net_iov *niov;
+		unsigned niov_idx, area_idx;
+
+		area_idx = rqe->off >> IORING_ZCRX_AREA_SHIFT;
+		niov_idx = (rqe->off & ~IORING_ZCRX_AREA_MASK) >> PAGE_SHIFT;
+
+		if (unlikely(rqe->__pad || area_idx))
+			continue;
+		area = ifq->area;
+
+		if (unlikely(niov_idx >= area->nia.num_niovs))
+			continue;
+		niov_idx = array_index_nospec(niov_idx, area->nia.num_niovs);
+
+		niov = &area->nia.niovs[niov_idx];
+		if (!io_zcrx_put_niov_uref(niov))
+			continue;
+
+		netmem = net_iov_to_netmem(niov);
+		if (page_pool_unref_netmem(netmem, 1) != 0)
+			continue;
+
+		if (unlikely(niov->pp != pp)) {
+			io_zcrx_return_niov(niov);
+			continue;
+		}
+
+		net_mp_netmem_place_in_cache(pp, netmem);
+	} while (--entries);
+
+	smp_store_release(&ifq->rq_ring->head, ifq->cached_rq_head);
+	spin_unlock_bh(&ifq->rq_lock);
+}
+
+static void io_zcrx_refill_slow(struct page_pool *pp, struct io_zcrx_ifq *ifq)
+{
+	struct io_zcrx_area *area = ifq->area;
+
+	spin_lock_bh(&area->freelist_lock);
+	while (area->free_count && pp->alloc.count < PP_ALLOC_CACHE_REFILL) {
+		struct net_iov *niov = __io_zcrx_get_free_niov(area);
+		netmem_ref netmem = net_iov_to_netmem(niov);
+
+		net_mp_niov_set_page_pool(pp, niov);
+		net_mp_netmem_place_in_cache(pp, netmem);
+	}
+	spin_unlock_bh(&area->freelist_lock);
+}
+
+static netmem_ref io_pp_zc_alloc_netmems(struct page_pool *pp, gfp_t gfp)
+{
+	struct io_zcrx_ifq *ifq = pp->mp_priv;
+
+	/* pp should already be ensuring that */
+	if (unlikely(pp->alloc.count))
+		goto out_return;
+
+	io_zcrx_ring_refill(pp, ifq);
+	if (likely(pp->alloc.count))
+		goto out_return;
+
+	io_zcrx_refill_slow(pp, ifq);
+	if (!pp->alloc.count)
+		return 0;
+out_return:
+	return pp->alloc.cache[--pp->alloc.count];
+}
+
+static bool io_pp_zc_release_netmem(struct page_pool *pp, netmem_ref netmem)
+{
+	struct net_iov *niov;
+
+	if (WARN_ON_ONCE(!netmem_is_net_iov(netmem)))
+		return false;
+
+	niov = netmem_to_net_iov(netmem);
+	net_mp_niov_clear_page_pool(niov);
+	io_zcrx_return_niov_freelist(niov);
+	return false;
+}
+
+static int io_pp_zc_init(struct page_pool *pp)
+{
+	struct io_zcrx_ifq *ifq = pp->mp_priv;
+
+	if (WARN_ON_ONCE(!ifq))
+		return -EINVAL;
+	if (WARN_ON_ONCE(ifq->dev != pp->slow.netdev))
+		return -EINVAL;
+	if (pp->dma_map)
+		return -EOPNOTSUPP;
+	if (pp->p.order != 0)
+		return -EOPNOTSUPP;
+
+	percpu_ref_get(&ifq->ctx->refs);
+	return 0;
+}
+
+static void io_pp_zc_destroy(struct page_pool *pp)
+{
+	struct io_zcrx_ifq *ifq = pp->mp_priv;
+	struct io_zcrx_area *area = ifq->area;
+
+	if (WARN_ON_ONCE(area->free_count != area->nia.num_niovs))
+		return;
+	percpu_ref_put(&ifq->ctx->refs);
+}
+
+static int io_pp_nl_fill(void *mp_priv, struct sk_buff *rsp,
+			 struct netdev_rx_queue *rxq)
+{
+	struct nlattr *nest;
+	int type;
+
+	type = rxq ? NETDEV_A_QUEUE_IO_URING : NETDEV_A_PAGE_POOL_IO_URING;
+	nest = nla_nest_start(rsp, type);
+	nla_nest_end(rsp, nest);
+
+	return 0;
+}
+
+static const struct memory_provider_ops io_uring_pp_zc_ops = {
+	.alloc_netmems		= io_pp_zc_alloc_netmems,
+	.release_netmem		= io_pp_zc_release_netmem,
+	.init			= io_pp_zc_init,
+	.destroy		= io_pp_zc_destroy,
+	.nl_fill		= io_pp_nl_fill,
+};
diff --git a/io_uring/zcrx.h b/io_uring/zcrx.h
index 46988a1dbd54..f31c8006ca9c 100644
--- a/io_uring/zcrx.h
+++ b/io_uring/zcrx.h
@@ -9,6 +9,7 @@
 struct io_zcrx_area {
 	struct net_iov_area	nia;
 	struct io_zcrx_ifq	*ifq;
+	atomic_t		*user_refs;
 
 	u16			area_id;
 	struct page		**pages;
@@ -26,6 +27,8 @@ struct io_zcrx_ifq {
 	struct io_uring			*rq_ring;
 	struct io_uring_zcrx_rqe	*rqes;
 	u32				rq_entries;
+	u32				cached_rq_head;
+	spinlock_t			rq_lock;
 
 	u32				if_rxq;
 	struct net_device		*dev;
-- 
2.43.5