// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/dma-map-ops.h>
#include <linux/mm.h>
#include <linux/nospec.h>
#include <linux/io_uring.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
#include <linux/skbuff_ref.h>
#include <linux/anon_inodes.h>

#include <net/page_pool/helpers.h>
#include <net/page_pool/memory_provider.h>
#include <net/netlink.h>
#include <net/netdev_queues.h>
#include <net/netdev_rx_queue.h>
#include <net/tcp.h>
#include <net/rps.h>

#include <trace/events/page_pool.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "kbuf.h"
#include "memmap.h"
#include "zcrx.h"
#include "rsrc.h"

#define IO_ZCRX_AREA_SUPPORTED_FLAGS	(IORING_ZCRX_AREA_DMABUF)

#define IO_DMA_ATTR (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING)

static inline struct io_zcrx_ifq *io_pp_to_ifq(struct page_pool *pp)
{
	return pp->mp_priv;
}

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 bool zcrx_set_ring_ctx(struct io_zcrx_ifq *zcrx,
			      struct io_ring_ctx *ctx)
{
	guard(spinlock_bh)(&zcrx->ctx_lock);
	if (zcrx->master_ctx)
		return false;
	percpu_ref_get(&ctx->refs);
	zcrx->master_ctx = ctx;
	return true;
}

static inline struct page *io_zcrx_iov_page(const struct net_iov *niov)
{
	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
	unsigned niov_pages_shift;

	lockdep_assert(!area->mem.is_dmabuf);

	niov_pages_shift = area->ifq->niov_shift - PAGE_SHIFT;
	return area->mem.pages[net_iov_idx(niov) << niov_pages_shift];
}

static int io_area_max_shift(struct io_zcrx_mem *mem)
{
	struct sg_table *sgt = mem->sgt;
	struct scatterlist *sg;
	unsigned shift = -1U;
	unsigned i;

	for_each_sgtable_dma_sg(sgt, sg, i)
		shift = min(shift, __ffs(sg_dma_len(sg)));
	return shift;
}

static int io_populate_area_dma(struct io_zcrx_ifq *ifq,
				struct io_zcrx_area *area)
{
	unsigned niov_size = 1U << ifq->niov_shift;
	struct sg_table *sgt = area->mem.sgt;
	struct scatterlist *sg;
	unsigned i, niov_idx = 0;

	for_each_sgtable_dma_sg(sgt, sg, i) {
		dma_addr_t dma = sg_dma_address(sg);
		unsigned long sg_len = sg_dma_len(sg);

		if (WARN_ON_ONCE(sg_len % niov_size))
			return -EINVAL;

		while (sg_len && niov_idx < area->nia.num_niovs) {
			struct net_iov *niov = &area->nia.niovs[niov_idx];

			if (net_mp_niov_set_dma_addr(niov, dma))
				return -EFAULT;
			sg_len -= niov_size;
			dma += niov_size;
			niov_idx++;
		}
	}

	if (WARN_ON_ONCE(niov_idx != area->nia.num_niovs))
		return -EFAULT;
	return 0;
}

static void io_release_dmabuf(struct io_zcrx_mem *mem)
{
	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
		return;

	if (mem->sgt)
		dma_buf_unmap_attachment_unlocked(mem->attach, mem->sgt,
						  DMA_FROM_DEVICE);
	if (mem->attach)
		dma_buf_detach(mem->dmabuf, mem->attach);
	if (mem->dmabuf)
		dma_buf_put(mem->dmabuf);

	mem->sgt = NULL;
	mem->attach = NULL;
	mem->dmabuf = NULL;
}

static int io_import_dmabuf(struct io_zcrx_ifq *ifq,
			    struct io_zcrx_mem *mem,
			    struct io_uring_zcrx_area_reg *area_reg)
{
	unsigned long off = (unsigned long)area_reg->addr;
	unsigned long len = (unsigned long)area_reg->len;
	unsigned long total_size = 0;
	struct scatterlist *sg;
	int dmabuf_fd = area_reg->dmabuf_fd;
	int i, ret;

	if (!ifq->dev)
		return -EINVAL;
	if (off)
		return -EINVAL;
	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
		return -EINVAL;

	mem->is_dmabuf = true;
	mem->dmabuf = dma_buf_get(dmabuf_fd);
	if (IS_ERR(mem->dmabuf)) {
		ret = PTR_ERR(mem->dmabuf);
		mem->dmabuf = NULL;
		goto err;
	}

	mem->attach = dma_buf_attach(mem->dmabuf, ifq->dev);
	if (IS_ERR(mem->attach)) {
		ret = PTR_ERR(mem->attach);
		mem->attach = NULL;
		goto err;
	}

	mem->sgt = dma_buf_map_attachment_unlocked(mem->attach, DMA_FROM_DEVICE);
	if (IS_ERR(mem->sgt)) {
		ret = PTR_ERR(mem->sgt);
		mem->sgt = NULL;
		goto err;
	}

	for_each_sgtable_dma_sg(mem->sgt, sg, i)
		total_size += sg_dma_len(sg);

	if (total_size != len) {
		ret = -EINVAL;
		goto err;
	}

	mem->size = len;
	return 0;
err:
	io_release_dmabuf(mem);
	return ret;
}

static unsigned long io_count_account_pages(struct page **pages, unsigned nr_pages)
{
	struct folio *last_folio = NULL;
	unsigned long res = 0;
	int i;

	for (i = 0; i < nr_pages; i++) {
		struct folio *folio = page_folio(pages[i]);

		if (folio == last_folio)
			continue;
		last_folio = folio;
		res += folio_nr_pages(folio);
	}
	return res;
}

static int io_import_umem(struct io_zcrx_ifq *ifq,
			  struct io_zcrx_mem *mem,
			  struct io_uring_zcrx_area_reg *area_reg)
{
	struct page **pages;
	int nr_pages, ret;
	bool mapped = false;

	if (area_reg->dmabuf_fd)
		return -EINVAL;
	if (!area_reg->addr)
		return -EFAULT;
	pages = io_pin_pages((unsigned long)area_reg->addr, area_reg->len,
				   &nr_pages);
	if (IS_ERR(pages))
		return PTR_ERR(pages);

	ret = sg_alloc_table_from_pages(&mem->page_sg_table, pages, nr_pages,
					0, (unsigned long)nr_pages << PAGE_SHIFT,
					GFP_KERNEL_ACCOUNT);
	if (ret)
		goto out_err;

	if (ifq->dev) {
		ret = dma_map_sgtable(ifq->dev, &mem->page_sg_table,
				      DMA_FROM_DEVICE, IO_DMA_ATTR);
		if (ret < 0)
			goto out_err;
		mapped = true;
	}

	mem->account_pages = io_count_account_pages(pages, nr_pages);
	ret = io_account_mem(ifq->user, ifq->mm_account, mem->account_pages);
	if (ret < 0) {
		mem->account_pages = 0;
		goto out_err;
	}

	mem->sgt = &mem->page_sg_table;
	mem->pages = pages;
	mem->nr_folios = nr_pages;
	mem->size = area_reg->len;
	return ret;
out_err:
	if (mapped)
		dma_unmap_sgtable(ifq->dev, &mem->page_sg_table,
				  DMA_FROM_DEVICE, IO_DMA_ATTR);
	sg_free_table(&mem->page_sg_table);
	unpin_user_pages(pages, nr_pages);
	kvfree(pages);
	return ret;
}

static void io_release_area_mem(struct io_zcrx_mem *mem)
{
	if (mem->is_dmabuf) {
		io_release_dmabuf(mem);
	} else if (mem->pages) {
		unpin_user_pages(mem->pages, mem->nr_folios);
		sg_free_table(mem->sgt);
		kvfree(mem->pages);
	}
	mem->pages = IO_URING_PTR_POISON;
	mem->sgt = IO_URING_PTR_POISON;
}

static int io_import_area(struct io_zcrx_ifq *ifq,
			  struct io_zcrx_mem *mem,
			  struct io_uring_zcrx_area_reg *area_reg)
{
	int ret;

	if (area_reg->flags & ~IO_ZCRX_AREA_SUPPORTED_FLAGS)
		return -EINVAL;
	if (area_reg->rq_area_token)
		return -EINVAL;
	if (area_reg->__resv2[0] || area_reg->__resv2[1])
		return -EINVAL;

	ret = io_validate_user_buf_range(area_reg->addr, area_reg->len);
	if (ret)
		return ret;
	if (area_reg->addr & ~PAGE_MASK || area_reg->len & ~PAGE_MASK)
		return -EINVAL;

	if (area_reg->flags & IORING_ZCRX_AREA_DMABUF)
		return io_import_dmabuf(ifq, mem, area_reg);
	return io_import_umem(ifq, mem, area_reg);
}

static void io_zcrx_unmap_area(struct io_zcrx_ifq *ifq,
				struct io_zcrx_area *area)
{
	int i;

	guard(mutex)(&ifq->pp_lock);
	if (!area->is_mapped)
		return;
	area->is_mapped = false;

	if (area->nia.niovs) {
		for (i = 0; i < area->nia.num_niovs; i++)
			net_mp_niov_set_dma_addr(&area->nia.niovs[i], 0);
	}

	if (area->mem.is_dmabuf) {
		io_release_dmabuf(&area->mem);
	} else {
		dma_unmap_sgtable(ifq->dev, &area->mem.page_sg_table,
				  DMA_FROM_DEVICE, IO_DMA_ATTR);
	}
}

static void zcrx_sync_for_device(struct page_pool *pp, struct io_zcrx_ifq *zcrx,
				 netmem_ref *netmems, unsigned nr)
{
#if defined(CONFIG_HAS_DMA) && defined(CONFIG_DMA_NEED_SYNC)
	struct device *dev = pp->p.dev;
	unsigned i, niov_size;
	dma_addr_t dma_addr;

	if (!dma_dev_need_sync(dev))
		return;
	niov_size = 1U << zcrx->niov_shift;

	for (i = 0; i < nr; i++) {
		dma_addr = page_pool_get_dma_addr_netmem(netmems[i]);
		__dma_sync_single_for_device(dev, dma_addr + pp->p.offset,
					     niov_size, pp->p.dma_dir);
	}
#endif
}

#define IO_RQ_MAX_ENTRIES		32768

#define IO_SKBS_PER_CALL_LIMIT	20

struct io_zcrx_args {
	struct io_kiocb		*req;
	struct io_zcrx_ifq	*ifq;
	unsigned		nr_skbs;
};

static const struct memory_provider_ops io_uring_pp_zc_ops;

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);
	int old;

	old = atomic_read(uref);
	do {
		if (unlikely(old == 0))
			return false;
	} while (!atomic_try_cmpxchg(uref, &old, old - 1));

	return true;
}

static void io_zcrx_get_niov_uref(struct net_iov *niov)
{
	atomic_inc(io_get_user_counter(niov));
}

static void io_fill_zcrx_offsets(struct io_uring_zcrx_offsets *offsets)
{
	offsets->head = offsetof(struct io_uring, head);
	offsets->tail = offsetof(struct io_uring, tail);
	offsets->rqes = ALIGN(sizeof(struct io_uring), L1_CACHE_BYTES);
}

static int io_allocate_rbuf_ring(struct io_ring_ctx *ctx,
				 struct io_zcrx_ifq *ifq,
				 struct io_uring_zcrx_ifq_reg *reg,
				 struct io_uring_region_desc *rd,
				 u32 id)
{
	u64 mmap_offset;
	size_t off, size;
	void *ptr;
	int ret;

	io_fill_zcrx_offsets(&reg->offsets);
	off = reg->offsets.rqes;
	size = off + sizeof(struct io_uring_zcrx_rqe) * reg->rq_entries;
	if (size > rd->size)
		return -EINVAL;

	mmap_offset = IORING_MAP_OFF_ZCRX_REGION;
	mmap_offset += (u64)id << IORING_OFF_ZCRX_SHIFT;

	ret = io_create_region(ctx, &ifq->rq_region, rd, mmap_offset);
	if (ret < 0)
		return ret;

	ptr = io_region_get_ptr(&ifq->rq_region);
	ifq->rq.ring = (struct io_uring *)ptr;
	ifq->rq.rqes = (struct io_uring_zcrx_rqe *)(ptr + off);

	memset(ifq->rq.ring, 0, sizeof(*ifq->rq.ring));
	return 0;
}

static void io_free_rbuf_ring(struct io_zcrx_ifq *ifq)
{
	io_free_region(ifq->user, &ifq->rq_region);
	ifq->rq.ring = IO_URING_PTR_POISON;
	ifq->rq.rqes = IO_URING_PTR_POISON;
	ifq->notif_stats = IO_URING_PTR_POISON;
}

static void io_zcrx_free_area(struct io_zcrx_ifq *ifq,
			      struct io_zcrx_area *area)
{
	io_zcrx_unmap_area(ifq, area);
	io_release_area_mem(&area->mem);

	if (area->mem.account_pages)
		io_unaccount_mem(ifq->user, ifq->mm_account,
				 area->mem.account_pages);

	kvfree(area->freelist);
	kvfree(area->nia.niovs);
	kvfree(area->user_refs);
	kfree(area);
}

static int io_zcrx_append_area(struct io_zcrx_ifq *ifq,
				struct io_zcrx_area *area)
{
	bool kern_readable = !area->mem.is_dmabuf;

	if (WARN_ON_ONCE(ifq->area))
		return -EINVAL;
	if (WARN_ON_ONCE(ifq->kern_readable != kern_readable))
		return -EINVAL;

	ifq->area = area;
	return 0;
}

static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
			       struct io_uring_zcrx_area_reg *area_reg,
			       struct io_uring_zcrx_ifq_reg *reg)
{
	int buf_size_shift = PAGE_SHIFT;
	struct io_zcrx_area *area;
	unsigned nr_iovs;
	int i, ret;

	if (reg->rx_buf_len) {
		if (!is_power_of_2(reg->rx_buf_len) ||
		     reg->rx_buf_len < PAGE_SIZE)
			return -EINVAL;
		buf_size_shift = ilog2(reg->rx_buf_len);
	}
	if (!ifq->dev && buf_size_shift != PAGE_SHIFT)
		return -EOPNOTSUPP;

	ret = -ENOMEM;
	area = kzalloc_obj(*area);
	if (!area)
		goto err;
	area->ifq = ifq;

	ret = io_import_area(ifq, &area->mem, area_reg);
	if (ret)
		goto err;
	if (ifq->dev)
		area->is_mapped = true;

	if (ifq->dev && buf_size_shift > io_area_max_shift(&area->mem)) {
		ret = -ERANGE;
		goto err;
	}

	ifq->niov_shift = buf_size_shift;
	nr_iovs = area->mem.size >> ifq->niov_shift;
	area->nia.num_niovs = nr_iovs;

	ret = -ENOMEM;
	area->nia.niovs = kvmalloc_objs(area->nia.niovs[0], nr_iovs,
					GFP_KERNEL_ACCOUNT | __GFP_ZERO);
	if (!area->nia.niovs)
		goto err;

	area->freelist = kvmalloc_array(nr_iovs, sizeof(area->freelist[0]),
					GFP_KERNEL_ACCOUNT | __GFP_ZERO);
	if (!area->freelist)
		goto err;

	area->user_refs = kvmalloc_objs(area->user_refs[0], nr_iovs,
					GFP_KERNEL_ACCOUNT | __GFP_ZERO);
	if (!area->user_refs)
		goto err;

	for (i = 0; i < nr_iovs; i++) {
		struct net_iov *niov = &area->nia.niovs[i];

		net_iov_init(niov, &area->nia, NET_IOV_IOURING);
		area->freelist[i] = i;
		atomic_set(&area->user_refs[i], 0);
	}

	if (ifq->dev) {
		ret = io_populate_area_dma(ifq, area);
		if (ret)
			goto err;
	}

	area->free_count = nr_iovs;
	/* we're only supporting one area per ifq for now */
	area->area_id = 0;
	area_reg->rq_area_token = (u64)area->area_id << IORING_ZCRX_AREA_SHIFT;
	spin_lock_init(&area->freelist_lock);

	ret = io_zcrx_append_area(ifq, area);
	if (!ret)
		return 0;
err:
	if (area)
		io_zcrx_free_area(ifq, area);
	return ret;
}

static struct io_zcrx_ifq *io_zcrx_ifq_alloc(struct io_ring_ctx *ctx)
{
	struct io_zcrx_ifq *ifq;

	ifq = kzalloc_obj(*ifq);
	if (!ifq)
		return NULL;

	ifq->if_rxq = -1;
	spin_lock_init(&ifq->ctx_lock);
	spin_lock_init(&ifq->rq.lock);
	mutex_init(&ifq->pp_lock);
	refcount_set(&ifq->refs, 1);
	refcount_set(&ifq->user_refs, 1);
	return ifq;
}

static void io_zcrx_drop_netdev(struct io_zcrx_ifq *ifq)
{
	guard(mutex)(&ifq->pp_lock);

	if (!ifq->netdev)
		return;
	netdev_put(ifq->netdev, &ifq->netdev_tracker);
	ifq->netdev = NULL;
}

static void io_close_queue(struct io_zcrx_ifq *ifq)
{
	struct net_device *netdev;
	netdevice_tracker netdev_tracker;
	struct pp_memory_provider_params p = {
		.mp_ops = &io_uring_pp_zc_ops,
		.mp_priv = ifq,
	};

	scoped_guard(mutex, &ifq->pp_lock) {
		netdev = ifq->netdev;
		netdev_tracker = ifq->netdev_tracker;
		ifq->netdev = NULL;
	}

	if (netdev) {
		if (ifq->if_rxq != -1) {
			netdev_lock(netdev);
			netif_mp_close_rxq(netdev, ifq->if_rxq, &p);
			netdev_unlock(netdev);
		}
		netdev_put(netdev, &netdev_tracker);
	}
	ifq->if_rxq = -1;
}

static void io_zcrx_ifq_free(struct io_zcrx_ifq *ifq)
{
	if (WARN_ON_ONCE(ifq->if_rxq != -1))
		return;
	if (WARN_ON_ONCE(ifq->netdev != NULL))
		return;
	if (WARN_ON_ONCE(ifq->master_ctx))
		return;

	if (ifq->area)
		io_zcrx_free_area(ifq, ifq->area);
	if (ifq->mm_account)
		mmdrop(ifq->mm_account);
	if (ifq->dev)
		put_device(ifq->dev);

	io_free_rbuf_ring(ifq);
	free_uid(ifq->user);
	mutex_destroy(&ifq->pp_lock);
	kfree(ifq);
}

static void io_put_zcrx_ifq(struct io_zcrx_ifq *ifq)
{
	if (refcount_dec_and_test(&ifq->refs))
		io_zcrx_ifq_free(ifq);
}

static void io_zcrx_return_niov_freelist(struct net_iov *niov)
{
	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);

	guard(spinlock_bh)(&area->freelist_lock);
	if (WARN_ON_ONCE(area->free_count >= area->nia.num_niovs))
		return;
	area->freelist[area->free_count++] = net_iov_idx(niov);
}

static struct net_iov *zcrx_get_free_niov(struct io_zcrx_area *area)
{
	unsigned niov_idx;

	lockdep_assert_held(&area->freelist_lock);

	if (unlikely(!area->free_count))
		return NULL;

	niov_idx = area->freelist[--area->free_count];
	return &area->nia.niovs[niov_idx];
}

static void io_zcrx_return_niov(struct net_iov *niov)
{
	netmem_ref netmem = net_iov_to_netmem(niov);

	if (!niov->desc.pp) {
		/* copy fallback allocated niovs */
		io_zcrx_return_niov_freelist(niov);
		return;
	}
	page_pool_put_unrefed_netmem(niov->desc.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);
	}
}

static void zcrx_unregister_user(struct io_zcrx_ifq *ifq, struct io_ring_ctx *ctx)
{
	scoped_guard(spinlock_bh, &ifq->ctx_lock) {
		if (ctx && ifq->master_ctx == ctx) {
			ifq->master_ctx = NULL;
			percpu_ref_put(&ctx->refs);
		}
	}

	if (refcount_dec_and_test(&ifq->user_refs)) {
		io_close_queue(ifq);
		io_zcrx_scrub(ifq);
	}
}

static void zcrx_unregister(struct io_zcrx_ifq *ifq, struct io_ring_ctx *ctx)
{
	zcrx_unregister_user(ifq, ctx);
	io_put_zcrx_ifq(ifq);
}

struct io_mapped_region *io_zcrx_get_region(struct io_ring_ctx *ctx,
					    unsigned int id)
{
	struct io_zcrx_ifq *ifq = xa_load(&ctx->zcrx_ctxs, id);

	lockdep_assert_held(&ctx->mmap_lock);

	return ifq ? &ifq->rq_region : NULL;
}

static int zcrx_box_release(struct inode *inode, struct file *file)
{
	struct io_zcrx_ifq *ifq = file->private_data;

	if (WARN_ON_ONCE(!ifq))
		return -EFAULT;
	zcrx_unregister(ifq, NULL);
	return 0;
}

static const struct file_operations zcrx_box_fops = {
	.owner		= THIS_MODULE,
	.release	= zcrx_box_release,
};

static int zcrx_export(struct io_ring_ctx *ctx, struct io_zcrx_ifq *ifq,
		       struct zcrx_ctrl *ctrl, void __user *arg)
{
	struct zcrx_ctrl_export *ce = &ctrl->zc_export;
	struct file *file;
	int fd;

	if (!mem_is_zero(ce, sizeof(*ce)))
		return -EINVAL;

	refcount_inc(&ifq->refs);
	refcount_inc(&ifq->user_refs);

	file = anon_inode_create_getfile("[zcrx]", &zcrx_box_fops,
					 ifq, O_CLOEXEC, NULL);
	if (IS_ERR(file)) {
		zcrx_unregister(ifq, NULL);
		return PTR_ERR(file);
	}

	fd = get_unused_fd_flags(O_CLOEXEC);
	if (fd < 0) {
		fput(file);
		return fd;
	}

	ce->zcrx_fd = fd;
	if (copy_to_user(arg, ctrl, sizeof(*ctrl))) {
		fput(file);
		put_unused_fd(fd);
		return -EFAULT;
	}

	fd_install(fd, file);
	return 0;
}

static int import_zcrx(struct io_ring_ctx *ctx,
		       struct io_uring_zcrx_ifq_reg __user *arg,
		       struct io_uring_zcrx_ifq_reg *reg)
{
	struct io_zcrx_ifq *ifq;
	struct file *file;
	int fd, ret;
	u32 id;

	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
		return -EINVAL;
	if (!(ctx->flags & (IORING_SETUP_CQE32|IORING_SETUP_CQE_MIXED)))
		return -EINVAL;
	if (reg->if_rxq || reg->rq_entries || reg->area_ptr || reg->region_ptr)
		return -EINVAL;
	if (reg->event_desc)
		return -EINVAL;
	if (reg->flags & ~ZCRX_REG_IMPORT)
		return -EINVAL;

	fd = reg->if_idx;
	CLASS(fd, f)(fd);
	if (fd_empty(f))
		return -EBADF;

	file = fd_file(f);
	if (file->f_op != &zcrx_box_fops || !file->private_data)
		return -EBADF;

	ifq = file->private_data;
	refcount_inc(&ifq->refs);
	refcount_inc(&ifq->user_refs);

	scoped_guard(mutex, &ctx->mmap_lock) {
		ret = xa_alloc(&ctx->zcrx_ctxs, &id, NULL, xa_limit_31b, GFP_KERNEL);
		if (ret)
			goto err;
	}

	reg->zcrx_id = id;
	io_fill_zcrx_offsets(&reg->offsets);
	if (copy_to_user(arg, reg, sizeof(*reg))) {
		ret = -EFAULT;
		goto err_xa_erase;
	}

	scoped_guard(mutex, &ctx->mmap_lock) {
		ret = -ENOMEM;
		if (xa_store(&ctx->zcrx_ctxs, id, ifq, GFP_KERNEL))
			goto err_xa_erase;
	}

	return 0;
err_xa_erase:
	scoped_guard(mutex, &ctx->mmap_lock)
		xa_erase(&ctx->zcrx_ctxs, id);
err:
	/* the import path never set the ->master_ctx ref, don't drop it */
	zcrx_unregister(ifq, NULL);
	return ret;
}

static int zcrx_register_netdev(struct io_zcrx_ifq *ifq,
				struct io_uring_zcrx_ifq_reg *reg,
				struct io_uring_zcrx_area_reg *area)
{
	struct pp_memory_provider_params mp_param = {};
	unsigned if_rxq = reg->if_rxq;
	int ret;

	ifq->netdev = netdev_get_by_index_lock(current->nsproxy->net_ns,
						reg->if_idx);
	if (!ifq->netdev)
		return -ENODEV;

	netdev_hold(ifq->netdev, &ifq->netdev_tracker, GFP_KERNEL);

	ifq->dev = netdev_queue_get_dma_dev(ifq->netdev, if_rxq, NETDEV_QUEUE_TYPE_RX);
	if (!ifq->dev) {
		ret = -EOPNOTSUPP;
		goto netdev_put_unlock;
	}
	get_device(ifq->dev);

	ret = io_zcrx_create_area(ifq, area, reg);
	if (ret)
		goto netdev_put_unlock;

	if (reg->rx_buf_len)
		mp_param.rx_page_size = 1U << ifq->niov_shift;
	mp_param.mp_ops = &io_uring_pp_zc_ops;
	mp_param.mp_priv = ifq;
	ret = netif_mp_open_rxq(ifq->netdev, if_rxq, &mp_param, NULL);
	if (ret)
		goto netdev_put_unlock;

	ifq->if_rxq = if_rxq;
	ret = 0;
netdev_put_unlock:
	netdev_unlock(ifq->netdev);
	return ret;
}

static int zcrx_validate_notif_stats(struct io_zcrx_ifq *ifq,
				     const struct io_uring_zcrx_ifq_reg *reg,
				     const struct zcrx_event_desc *notif)
{
	size_t stats_off = notif->stats_offset;
	size_t used, end;

	used = reg->offsets.rqes +
	       sizeof(struct io_uring_zcrx_rqe) * reg->rq_entries;

	if (!IS_ALIGNED(stats_off, __alignof__(struct zcrx_stats)))
		return -EINVAL;
	if (stats_off < used)
		return -ERANGE;
	if (check_add_overflow(stats_off,
			       	sizeof(struct zcrx_stats),
			       &end))
		return -ERANGE;
	if (end > io_region_size(&ifq->rq_region))
		return -ERANGE;

	ifq->notif_stats = io_region_get_ptr(&ifq->rq_region) + stats_off;
	memset(ifq->notif_stats, 0, sizeof(*ifq->notif_stats));

	return 0;
}

int io_register_zcrx(struct io_ring_ctx *ctx,
		     struct io_uring_zcrx_ifq_reg __user *arg)
{
	struct zcrx_event_desc notif;
	struct io_uring_zcrx_area_reg area;
	struct io_uring_zcrx_ifq_reg reg;
	struct io_uring_region_desc rd;
	struct io_zcrx_ifq *ifq;
	int ret;
	u32 id;

	/*
	 * 1. Interface queue allocation.
	 * 2. It can observe data destined for sockets of other tasks.
	 */
	if (!capable(CAP_NET_ADMIN))
		return -EPERM;

	/* mandatory io_uring features for zc rx */
	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
		return -EINVAL;
	if (!(ctx->flags & (IORING_SETUP_CQE32|IORING_SETUP_CQE_MIXED)))
		return -EINVAL;
	if (copy_from_user(&reg, arg, sizeof(reg)))
		return -EFAULT;
	if (!mem_is_zero(&reg.__resv, sizeof(reg.__resv)) || reg.zcrx_id)
		return -EINVAL;
	if (reg.flags & ~ZCRX_SUPPORTED_REG_FLAGS)
		return -EINVAL;
	if (reg.flags & ZCRX_REG_IMPORT)
		return import_zcrx(ctx, arg, &reg);
	if (copy_from_user(&rd, u64_to_user_ptr(reg.region_ptr), sizeof(rd)))
		return -EFAULT;
	if (reg.if_rxq == -1 || !reg.rq_entries)
		return -EINVAL;
	if ((reg.if_rxq || reg.if_idx) && (reg.flags & ZCRX_REG_NODEV))
		return -EINVAL;
	if (reg.rq_entries > IO_RQ_MAX_ENTRIES) {
		if (!(ctx->flags & IORING_SETUP_CLAMP))
			return -EINVAL;
		reg.rq_entries = IO_RQ_MAX_ENTRIES;
	}
	reg.rq_entries = roundup_pow_of_two(reg.rq_entries);

	if (copy_from_user(&area, u64_to_user_ptr(reg.area_ptr), sizeof(area)))
		return -EFAULT;

	memset(&notif, 0, sizeof(notif));
	if (reg.event_desc && copy_from_user(&notif, u64_to_user_ptr(reg.event_desc),
					     sizeof(notif)))
		return -EFAULT;
	if (notif.type_mask & ~ZCRX_EVENT_TYPE_MASK)
		return -EINVAL;
	if (notif.flags & ~ZCRX_EVENT_DESC_FLAG_STATS)
		return -EINVAL;
	if (!(notif.flags & ZCRX_EVENT_DESC_FLAG_STATS)) {
		if (notif.stats_offset)
			return -EINVAL;
	}
	if (!mem_is_zero(&notif.__resv2, sizeof(notif.__resv2)))
		return -EINVAL;

	ifq = io_zcrx_ifq_alloc(ctx);
	if (!ifq)
		return -ENOMEM;

	ifq->notif_data = notif.user_data;
	ifq->allowed_notif_mask = notif.type_mask;

	if (ctx->user) {
		get_uid(ctx->user);
		ifq->user = ctx->user;
	}
	if (ctx->mm_account) {
		mmgrab(ctx->mm_account);
		ifq->mm_account = ctx->mm_account;
	}
	ifq->rq.nr_entries = reg.rq_entries;

	scoped_guard(mutex, &ctx->mmap_lock) {
		/* preallocate id */
		ret = xa_alloc(&ctx->zcrx_ctxs, &id, NULL, xa_limit_31b, GFP_KERNEL);
		if (ret)
			goto ifq_free;
	}

	ret = io_allocate_rbuf_ring(ctx, ifq, &reg, &rd, id);
	if (ret)
		goto err;

	if (notif.flags & ZCRX_EVENT_DESC_FLAG_STATS) {
		ret = zcrx_validate_notif_stats(ifq, &reg, &notif);
		if (ret)
			goto err;
	}

	ifq->kern_readable = !(area.flags & IORING_ZCRX_AREA_DMABUF);

	if (!(reg.flags & ZCRX_REG_NODEV)) {
		ret = zcrx_register_netdev(ifq, &reg, &area);
		if (ret)
			goto err;
	} else {
		ret = io_zcrx_create_area(ifq, &area, &reg);
		if (ret)
			goto err;
	}

	reg.zcrx_id = id;

	scoped_guard(mutex, &ctx->mmap_lock) {
		/* publish ifq */
		ret = -ENOMEM;
		if (xa_store(&ctx->zcrx_ctxs, id, ifq, GFP_KERNEL))
			goto err;
	}

	reg.rx_buf_len = 1U << ifq->niov_shift;

	if (copy_to_user(arg, &reg, sizeof(reg)) ||
	    copy_to_user(u64_to_user_ptr(reg.region_ptr), &rd, sizeof(rd)) ||
	    copy_to_user(u64_to_user_ptr(reg.area_ptr), &area, sizeof(area))) {
		ret = -EFAULT;
		goto err;
	}

	if (notif.type_mask)
		zcrx_set_ring_ctx(ifq, ctx);
	return 0;
err:
	scoped_guard(mutex, &ctx->mmap_lock)
		xa_erase(&ctx->zcrx_ctxs, id);
ifq_free:
	zcrx_unregister(ifq, ctx);
	return ret;
}

static inline bool is_zcrx_entry_marked(struct io_ring_ctx *ctx, unsigned long id)
{
	return xa_get_mark(&ctx->zcrx_ctxs, id, XA_MARK_1);
}

static inline void set_zcrx_entry_mark(struct io_ring_ctx *ctx, unsigned long id)
{
	xa_set_mark(&ctx->zcrx_ctxs, id, XA_MARK_1);
}

void io_terminate_zcrx(struct io_ring_ctx *ctx)
{
	struct io_zcrx_ifq *ifq;
	unsigned long id = 0;

	lockdep_assert_held(&ctx->uring_lock);

	while (1) {
		scoped_guard(mutex, &ctx->mmap_lock)
			ifq = xa_find(&ctx->zcrx_ctxs, &id, ULONG_MAX, XA_PRESENT);
		if (!ifq)
			break;
		if (WARN_ON_ONCE(is_zcrx_entry_marked(ctx, id)))
			break;
		set_zcrx_entry_mark(ctx, id);
		id++;
		zcrx_unregister_user(ifq, ctx);
	}
}

void io_unregister_zcrx(struct io_ring_ctx *ctx)
{
	struct io_zcrx_ifq *ifq;

	lockdep_assert_held(&ctx->uring_lock);

	while (1) {
		scoped_guard(mutex, &ctx->mmap_lock) {
			unsigned long id = 0;

			ifq = xa_find(&ctx->zcrx_ctxs, &id, ULONG_MAX, XA_PRESENT);
			if (ifq) {
				if (WARN_ON_ONCE(!is_zcrx_entry_marked(ctx, id))) {
					ifq = NULL;
					break;
				}
				xa_erase(&ctx->zcrx_ctxs, id);
			}
		}
		if (!ifq)
			break;
		/*
		 * io_uring can run requests and return buffers to the user
		 * after termination, scrub it again.
		 */
		if (refcount_read(&ifq->user_refs) == 0)
			io_zcrx_scrub(ifq);
		io_put_zcrx_ifq(ifq);
	}

	xa_destroy(&ctx->zcrx_ctxs);
}

static inline u32 zcrx_rq_entries(struct zcrx_rq *rq)
{
	u32 entries;

	entries = smp_load_acquire(&rq->ring->tail) - rq->cached_head;
	return min(entries, rq->nr_entries);
}

static struct io_uring_zcrx_rqe *zcrx_next_rqe(struct zcrx_rq *rq, unsigned mask)
{
	unsigned int idx = rq->cached_head++ & mask;

	return &rq->rqes[idx];
}

static inline bool io_parse_rqe(struct io_uring_zcrx_rqe *rqe,
				struct io_zcrx_ifq *ifq,
				struct net_iov **ret_niov)
{
	__u64 off = READ_ONCE(rqe->off);
	unsigned niov_idx, area_idx;
	struct io_zcrx_area *area;

	area_idx = off >> IORING_ZCRX_AREA_SHIFT;
	niov_idx = (off & ~IORING_ZCRX_AREA_MASK) >> ifq->niov_shift;

	if (unlikely(rqe->__pad || area_idx))
		return false;
	area = ifq->area;

	if (unlikely(niov_idx >= area->nia.num_niovs))
		return false;
	niov_idx = array_index_nospec(niov_idx, area->nia.num_niovs);

	*ret_niov = &area->nia.niovs[niov_idx];
	return true;
}

static unsigned io_zcrx_ring_refill(struct page_pool *pp,
				    struct io_zcrx_ifq *ifq,
				    netmem_ref *netmems, unsigned to_alloc)
{
	struct zcrx_rq *rq = &ifq->rq;
	unsigned int mask = rq->nr_entries - 1;
	unsigned int entries;
	unsigned allocated = 0;

	guard(spinlock_bh)(&rq->lock);

	entries = zcrx_rq_entries(rq);
	entries = min_t(unsigned, entries, to_alloc);
	if (unlikely(!entries))
		return 0;

	do {
		struct io_uring_zcrx_rqe *rqe = zcrx_next_rqe(rq, mask);
		struct net_iov *niov;
		netmem_ref netmem;

		if (!io_parse_rqe(rqe, ifq, &niov))
			continue;
		if (!io_zcrx_put_niov_uref(niov))
			continue;

		netmem = net_iov_to_netmem(niov);
		if (!page_pool_unref_and_test(netmem))
			continue;

		if (unlikely(niov->desc.pp != pp)) {
			io_zcrx_return_niov(niov);
			continue;
		}

		netmems[allocated] = netmem;
		allocated++;
	} while (--entries);

	smp_store_release(&rq->ring->head, rq->cached_head);
	return allocated;
}

static unsigned io_zcrx_refill_slow(struct page_pool *pp, struct io_zcrx_ifq *ifq,
				    netmem_ref *netmems, unsigned to_alloc)
{
	struct io_zcrx_area *area = ifq->area;
	unsigned allocated = 0;

	guard(spinlock_bh)(&area->freelist_lock);

	for (allocated = 0; allocated < to_alloc; allocated++) {
		struct net_iov *niov = zcrx_get_free_niov(area);

		if (!niov)
			break;
		net_mp_niov_set_page_pool(pp, niov);
		netmems[allocated] = net_iov_to_netmem(niov);
	}
	return allocated;
}

static void zcrx_notif_tw(struct io_tw_req tw_req, io_tw_token_t tw)
{
	struct io_kiocb *req = tw_req.req;
	struct io_ring_ctx *ctx = req->ctx;

	io_post_aux_cqe(ctx, req->cqe.user_data, req->cqe.res, 0);
	percpu_ref_put(&ctx->refs);
	io_poison_req(req);
	kmem_cache_free(req_cachep, req);
}

static void zcrx_stat_add(__u64 *p, s64 v)
{
	WRITE_ONCE(*p, READ_ONCE(*p) + v);
}

static void zcrx_send_notif(struct io_zcrx_ifq *ifq, unsigned type)
{
	gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN | __GFP_ZERO;
	u32 type_mask = 1 << type;
	struct io_kiocb *req;

	if (!(type_mask & ifq->allowed_notif_mask))
		return;

	guard(spinlock_bh)(&ifq->ctx_lock);
	if (!ifq->master_ctx)
		return;
	if (type_mask & ifq->fired_notifs)
		return;

	req = kmem_cache_alloc(req_cachep, gfp);
	if (unlikely(!req))
		return;

	ifq->fired_notifs |= type_mask;

	req->opcode = IORING_OP_NOP;
	req->cqe.user_data = ifq->notif_data;
	req->cqe.res = type;
	req->ctx = ifq->master_ctx;
	percpu_ref_get(&req->ctx->refs);
	req->tctx = NULL;
	req->io_task_work.func = zcrx_notif_tw;
	io_req_task_work_add(req);
}

static netmem_ref io_pp_zc_alloc_netmems(struct page_pool *pp, gfp_t gfp)
{
	struct io_zcrx_ifq *ifq = io_pp_to_ifq(pp);
	netmem_ref *netmems = pp->alloc.cache;
	unsigned to_alloc = PP_ALLOC_CACHE_REFILL;
	unsigned allocated;

	/* pp should already be ensuring that */
	if (WARN_ON_ONCE(pp->alloc.count))
		return 0;

	allocated = io_zcrx_ring_refill(pp, ifq, netmems, to_alloc);
	if (likely(allocated))
		goto out_return;

	allocated = io_zcrx_refill_slow(pp, ifq, netmems, to_alloc);
	if (!allocated) {
		zcrx_send_notif(ifq, ZCRX_EVENT_ALLOC_FAIL);
		return 0;
	}
out_return:
	zcrx_sync_for_device(pp, ifq, netmems, allocated);
	allocated--;
	pp->alloc.count += allocated;
	return netmems[allocated];
}

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 = io_pp_to_ifq(pp);

	if (WARN_ON_ONCE(!ifq))
		return -EINVAL;
	if (WARN_ON_ONCE(ifq->dev != pp->p.dev))
		return -EINVAL;
	if (WARN_ON_ONCE(!pp->dma_map))
		return -EOPNOTSUPP;
	if (pp->p.order + PAGE_SHIFT != ifq->niov_shift)
		return -EINVAL;
	if (pp->p.dma_dir != DMA_FROM_DEVICE)
		return -EOPNOTSUPP;

	refcount_inc(&ifq->refs);
	return 0;
}

static void io_pp_zc_destroy(struct page_pool *pp)
{
	io_put_zcrx_ifq(io_pp_to_ifq(pp));
}

static int io_pp_nl_fill(void *mp_priv, struct sk_buff *rsp,
			 struct netdev_rx_queue *rxq)
{
	struct io_zcrx_ifq *ifq = mp_priv;
	struct nlattr *nest;
	int type;

	type = rxq ? NETDEV_A_QUEUE_IO_URING : NETDEV_A_PAGE_POOL_IO_URING;
	nest = nla_nest_start(rsp, type);
	if (!nest)
		return -EMSGSIZE;

	if (nla_put_uint(rsp, NETDEV_A_IO_URING_PROVIDER_INFO_RX_BUF_LEN,
			 1ULL << ifq->niov_shift)) {
		nla_nest_cancel(rsp, nest);
		return -EMSGSIZE;
	}

	nla_nest_end(rsp, nest);

	return 0;
}

static void io_pp_uninstall(void *mp_priv, struct netdev_rx_queue *rxq)
{
	struct pp_memory_provider_params *p = &rxq->mp_params;
	struct io_zcrx_ifq *ifq = mp_priv;

	io_zcrx_drop_netdev(ifq);
	if (ifq->area)
		io_zcrx_unmap_area(ifq, ifq->area);

	p->mp_ops = NULL;
	p->mp_priv = NULL;
}

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,
	.uninstall		= io_pp_uninstall,
};

static unsigned zcrx_parse_rq(netmem_ref *netmem_array, unsigned nr,
			      struct io_zcrx_ifq *zcrx, struct zcrx_rq *rq)
{
	unsigned int mask = rq->nr_entries - 1;
	unsigned int i;

	nr = min(nr, zcrx_rq_entries(rq));
	for (i = 0; i < nr; i++) {
		struct io_uring_zcrx_rqe *rqe = zcrx_next_rqe(rq, mask);
		struct net_iov *niov;

		if (!io_parse_rqe(rqe, zcrx, &niov))
			break;
		netmem_array[i] = net_iov_to_netmem(niov);
	}

	smp_store_release(&rq->ring->head, rq->cached_head);
	return i;
}

#define ZCRX_FLUSH_BATCH 32

static void zcrx_return_buffers(netmem_ref *netmems, unsigned nr)
{
	unsigned i;

	for (i = 0; i < nr; i++) {
		netmem_ref netmem = netmems[i];
		struct net_iov *niov = netmem_to_net_iov(netmem);

		if (!io_zcrx_put_niov_uref(niov))
			continue;
		if (!page_pool_unref_and_test(netmem))
			continue;
		io_zcrx_return_niov(niov);
	}
}

static int zcrx_flush_rq(struct io_ring_ctx *ctx, struct io_zcrx_ifq *zcrx,
			 struct zcrx_ctrl *ctrl)
{
	struct zcrx_ctrl_flush_rq *frq = &ctrl->zc_flush;
	netmem_ref netmems[ZCRX_FLUSH_BATCH];
	unsigned total = 0;
	unsigned nr;

	if (!mem_is_zero(&frq->__resv, sizeof(frq->__resv)))
		return -EINVAL;

	do {
		struct zcrx_rq *rq = &zcrx->rq;

		scoped_guard(spinlock_bh, &rq->lock) {
			nr = zcrx_parse_rq(netmems, ZCRX_FLUSH_BATCH, zcrx, rq);
			zcrx_return_buffers(netmems, nr);
		}

		total += nr;

		if (fatal_signal_pending(current))
			break;
		cond_resched();
	} while (nr == ZCRX_FLUSH_BATCH && total < zcrx->rq.nr_entries);

	return 0;
}

static int zcrx_arm_notif(struct io_ring_ctx *ctx, struct io_zcrx_ifq *zcrx,
			  struct zcrx_ctrl *ctrl)
{
	const struct zcrx_ctrl_arm_event *an = &ctrl->zc_arm_event;
	unsigned type_mask;

	if (an->event_type >= __ZCRX_EVENT_TYPE_LAST)
		return -EINVAL;
	if (!mem_is_zero(&an->__resv, sizeof(an->__resv)))
		return -EINVAL;

	guard(spinlock_bh)(&zcrx->ctx_lock);
	type_mask = 1U << an->event_type;
	if (type_mask & ~zcrx->fired_notifs)
		return -EINVAL;
	zcrx->fired_notifs &= ~type_mask;
	return 0;
}

int io_zcrx_ctrl(struct io_ring_ctx *ctx, void __user *arg, unsigned nr_args)
{
	struct zcrx_ctrl ctrl;
	struct io_zcrx_ifq *zcrx;

	BUILD_BUG_ON(sizeof(ctrl.zc_export) != sizeof(ctrl.zc_flush));
	BUILD_BUG_ON(sizeof(ctrl.zc_export) != sizeof(ctrl.zc_arm_event));

	if (nr_args)
		return -EINVAL;
	if (copy_from_user(&ctrl, arg, sizeof(ctrl)))
		return -EFAULT;
	if (!mem_is_zero(&ctrl.__resv, sizeof(ctrl.__resv)))
		return -EFAULT;

	zcrx = xa_load(&ctx->zcrx_ctxs, ctrl.zcrx_id);
	if (!zcrx)
		return -ENXIO;

	switch (ctrl.op) {
	case ZCRX_CTRL_FLUSH_RQ:
		return zcrx_flush_rq(ctx, zcrx, &ctrl);
	case ZCRX_CTRL_EXPORT:
		return zcrx_export(ctx, zcrx, &ctrl, arg);
	case ZCRX_CTRL_ARM_EVENT:
		return zcrx_arm_notif(ctx, zcrx, &ctrl);
	}

	return -EOPNOTSUPP;
}

static bool io_zcrx_queue_cqe(struct io_kiocb *req, struct net_iov *niov,
			      struct io_zcrx_ifq *ifq, int off, int len)
{
	struct io_ring_ctx *ctx = req->ctx;
	struct io_uring_zcrx_cqe *rcqe;
	struct io_zcrx_area *area;
	struct io_uring_cqe *cqe;
	u64 offset;

	if (!io_defer_get_uncommited_cqe(ctx, &cqe))
		return false;

	cqe->user_data = req->cqe.user_data;
	cqe->res = len;
	cqe->flags = IORING_CQE_F_MORE;
	if (ctx->flags & IORING_SETUP_CQE_MIXED)
		cqe->flags |= IORING_CQE_F_32;

	area = io_zcrx_iov_to_area(niov);
	offset = off + (net_iov_idx(niov) << ifq->niov_shift);
	rcqe = (struct io_uring_zcrx_cqe *)(cqe + 1);
	rcqe->off = offset + ((u64)area->area_id << IORING_ZCRX_AREA_SHIFT);
	rcqe->__pad = 0;
	return true;
}

static struct net_iov *io_alloc_fallback_niov(struct io_zcrx_ifq *ifq)
{
	struct io_zcrx_area *area = ifq->area;
	struct net_iov *niov = NULL;

	if (!ifq->kern_readable)
		return NULL;

	scoped_guard(spinlock_bh, &area->freelist_lock)
		niov = zcrx_get_free_niov(area);

	if (niov)
		page_pool_fragment_netmem(net_iov_to_netmem(niov), 1);
	return niov;
}

struct io_copy_cache {
	struct page		*page;
	unsigned long		offset;
	size_t			size;
};

static ssize_t io_copy_page(struct io_copy_cache *cc, struct page *src_page,
			    unsigned int src_offset, size_t len)
{
	size_t copied = 0;

	len = min(len, cc->size);

	while (len) {
		void *src_addr, *dst_addr;
		struct page *dst_page = cc->page;
		unsigned dst_offset = cc->offset;
		size_t n = len;

		if (folio_test_partial_kmap(page_folio(dst_page)) ||
		    folio_test_partial_kmap(page_folio(src_page))) {
			dst_page += dst_offset / PAGE_SIZE;
			dst_offset = offset_in_page(dst_offset);
			src_page += src_offset / PAGE_SIZE;
			src_offset = offset_in_page(src_offset);
			n = min(PAGE_SIZE - src_offset, PAGE_SIZE - dst_offset);
			n = min(n, len);
		}

		dst_addr = kmap_local_page(dst_page) + dst_offset;
		src_addr = kmap_local_page(src_page) + src_offset;

		memcpy(dst_addr, src_addr, n);

		kunmap_local(src_addr);
		kunmap_local(dst_addr);

		cc->size -= n;
		cc->offset += n;
		src_offset += n;
		len -= n;
		copied += n;
	}
	return copied;
}

static ssize_t io_zcrx_copy_chunk(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
				  struct page *src_page, unsigned int src_offset,
				  size_t len)
{
	size_t copied = 0;
	int ret = 0;

	while (len) {
		struct io_copy_cache cc;
		struct net_iov *niov;
		size_t n;

		niov = io_alloc_fallback_niov(ifq);
		if (!niov) {
			ret = -ENOMEM;
			break;
		}

		cc.page = io_zcrx_iov_page(niov);
		cc.offset = 0;
		cc.size = PAGE_SIZE;

		n = io_copy_page(&cc, src_page, src_offset, len);

		if (!io_zcrx_queue_cqe(req, niov, ifq, 0, n)) {
			io_zcrx_return_niov(niov);
			ret = -ENOSPC;
			break;
		}

		io_zcrx_get_niov_uref(niov);
		src_offset += n;
		len -= n;
		copied += n;
	}

	return copied ? copied : ret;
}

static int io_zcrx_copy_frag(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
			     const skb_frag_t *frag, int off, int len)
{
	struct page *page = skb_frag_page(frag);
	int ret;

	ret = io_zcrx_copy_chunk(req, ifq, page, off + skb_frag_off(frag), len);
	if (ret > 0) {
		if (ifq->notif_stats) {
			zcrx_stat_add(&ifq->notif_stats->copy_count, 1);
			zcrx_stat_add(&ifq->notif_stats->copy_bytes, ret);
		}
		zcrx_send_notif(ifq, ZCRX_EVENT_COPY);
	}

	return 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)
{
	struct net_iov *niov;
	struct page_pool *pp;

	if (unlikely(!skb_frag_is_net_iov(frag)))
		return io_zcrx_copy_frag(req, ifq, frag, off, len);

	niov = netmem_to_net_iov(frag->netmem);
	pp = niov->desc.pp;

	if (!pp || pp->mp_ops != &io_uring_pp_zc_ops || io_pp_to_ifq(pp) != ifq)
		return -EFAULT;

	if (!io_zcrx_queue_cqe(req, niov, ifq, off + skb_frag_off(frag), len))
		return -ENOSPC;

	/*
	 * Prevent it from being recycled while user is accessing it.
	 * It has to be done before grabbing a user reference.
	 */
	page_pool_ref_netmem(net_iov_to_netmem(niov));
	io_zcrx_get_niov_uref(niov);
	return len;
}

static int
io_zcrx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
		 unsigned int offset, size_t len)
{
	struct io_zcrx_args *args = desc->arg.data;
	struct io_zcrx_ifq *ifq = args->ifq;
	struct io_kiocb *req = args->req;
	struct sk_buff *frag_iter;
	unsigned start, start_off = offset;
	int i, copy, end, off;
	int ret = 0;

	len = min_t(size_t, len, desc->count);
	/*
	 * __tcp_read_sock() always calls io_zcrx_recv_skb one last time, even
	 * if desc->count is already 0. This is caused by the if (offset + 1 !=
	 * skb->len) check. Return early in this case to break out of
	 * __tcp_read_sock().
	 */
	if (!len)
		return 0;
	if (unlikely(args->nr_skbs++ > IO_SKBS_PER_CALL_LIMIT))
		return -EAGAIN;

	if (unlikely(offset < skb_headlen(skb))) {
		ssize_t copied;
		size_t to_copy;

		to_copy = min_t(size_t, skb_headlen(skb) - offset, len);
		copied = io_zcrx_copy_chunk(req, ifq, virt_to_page(skb->data),
					    offset_in_page(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;

		if (WARN_ON(start > offset + len))
			return -EFAULT;

		frag = &skb_shinfo(skb)->frags[i];
		end = start + skb_frag_size(frag);

		if (offset < end) {
			copy = end - offset;
			if (copy > len)
				copy = len;

			off = offset - start;
			ret = io_zcrx_recv_frag(req, ifq, frag, off, copy);
			if (ret < 0)
				goto out;

			offset += ret;
			len -= ret;
			if (len == 0 || ret != copy)
				goto out;
		}
		start = end;
	}

	skb_walk_frags(skb, frag_iter) {
		if (WARN_ON(start > offset + len))
			return -EFAULT;

		end = start + frag_iter->len;
		if (offset < end) {
			size_t count;

			copy = end - offset;
			if (copy > len)
				copy = len;

			off = offset - start;
			count = desc->count;
			ret = io_zcrx_recv_skb(desc, frag_iter, off, copy);
			desc->count = count;
			if (ret < 0)
				goto out;

			offset += ret;
			len -= ret;
			if (len == 0 || ret != copy)
				goto out;
		}
		start = end;
	}

out:
	if (offset == start_off)
		return ret;
	desc->count -= (offset - start_off);
	return offset - start_off;
}

static int io_zcrx_tcp_recvmsg(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
				struct sock *sk, int flags,
				unsigned issue_flags, unsigned int *outlen)
{
	unsigned int len = *outlen;
	struct io_zcrx_args args = {
		.req = req,
		.ifq = ifq,
	};
	read_descriptor_t rd_desc = {
		.count = len ? len : UINT_MAX,
		.arg.data = &args,
	};
	int ret;

	lock_sock(sk);
	ret = tcp_read_sock(sk, &rd_desc, io_zcrx_recv_skb);
	if (len && ret > 0)
		*outlen = len - ret;
	if (ret <= 0) {
		if (ret < 0 || sock_flag(sk, SOCK_DONE))
			goto out;
		if (sk->sk_err)
			ret = sock_error(sk);
		else if (sk->sk_shutdown & RCV_SHUTDOWN)
			goto out;
		else if (sk->sk_state == TCP_CLOSE)
			ret = -ENOTCONN;
		else
			ret = -EAGAIN;
	} else if (unlikely(args.nr_skbs > IO_SKBS_PER_CALL_LIMIT) &&
		   (issue_flags & IO_URING_F_MULTISHOT)) {
		ret = IOU_REQUEUE;
	} else if (sock_flag(sk, SOCK_DONE)) {
		/* Make it to retry until it finally gets 0. */
		if (issue_flags & IO_URING_F_MULTISHOT)
			ret = IOU_REQUEUE;
		else
			ret = -EAGAIN;
	}
out:
	release_sock(sk);
	return ret;
}

int io_zcrx_recv(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
		 struct socket *sock, unsigned int flags,
		 unsigned issue_flags, unsigned int *len)
{
	struct sock *sk = sock->sk;
	const struct proto *prot = READ_ONCE(sk->sk_prot);

	if (prot->recvmsg != tcp_recvmsg)
		return -EPROTONOSUPPORT;

	sock_rps_record_flow(sk);
	return io_zcrx_tcp_recvmsg(req, ifq, sk, flags, issue_flags, len);
}