Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1894 insertions, 0 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
new file mode 100644
index 000000000..c3ca28ca6
--- /dev/null
+++ b/lib/iov_iter.c
@@ -0,0 +1,1894 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <crypto/hash.h>
+#include <linux/export.h>
+#include <linux/bvec.h>
+#include <linux/fault-inject-usercopy.h>
+#include <linux/uio.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/splice.h>
+#include <linux/compat.h>
+#include <net/checksum.h>
+#include <linux/scatterlist.h>
+#include <linux/instrumented.h>
+
+#define PIPE_PARANOIA /* for now */
+
+/* covers ubuf and kbuf alike */
+#define iterate_buf(i, n, base, len, off, __p, STEP) {		\
+	size_t __maybe_unused off = 0;				\
+	len = n;						\
+	base = __p + i->iov_offset;				\
+	len -= (STEP);						\
+	i->iov_offset += len;					\
+	n = len;						\
+}
+
+/* covers iovec and kvec alike */
+#define iterate_iovec(i, n, base, len, off, __p, STEP) {	\
+	size_t off = 0;						\
+	size_t skip = i->iov_offset;				\
+	do {							\
+		len = min(n, __p->iov_len - skip);		\
+		if (likely(len)) {				\
+			base = __p->iov_base + skip;		\
+			len -= (STEP);				\
+			off += len;				\
+			skip += len;				\
+			n -= len;				\
+			if (skip < __p->iov_len)		\
+				break;				\
+		}						\
+		__p++;						\
+		skip = 0;					\
+	} while (n);						\
+	i->iov_offset = skip;					\
+	n = off;						\
+}
+
+#define iterate_bvec(i, n, base, len, off, p, STEP) {		\
+	size_t off = 0;						\
+	unsigned skip = i->iov_offset;				\
+	while (n) {						\
+		unsigned offset = p->bv_offset + skip;		\
+		unsigned left;					\
+		void *kaddr = kmap_local_page(p->bv_page +	\
+					offset / PAGE_SIZE);	\
+		base = kaddr + offset % PAGE_SIZE;		\
+		len = min(min(n, (size_t)(p->bv_len - skip)),	\
+		     (size_t)(PAGE_SIZE - offset % PAGE_SIZE));	\
+		left = (STEP);					\
+		kunmap_local(kaddr);				\
+		len -= left;					\
+		off += len;					\
+		skip += len;					\
+		if (skip == p->bv_len) {			\
+			skip = 0;				\
+			p++;					\
+		}						\
+		n -= len;					\
+		if (left)					\
+			break;					\
+	}							\
+	i->iov_offset = skip;					\
+	n = off;						\
+}
+
+#define iterate_xarray(i, n, base, len, __off, STEP) {		\
+	__label__ __out;					\
+	size_t __off = 0;					\
+	struct folio *folio;					\
+	loff_t start = i->xarray_start + i->iov_offset;		\
+	pgoff_t index = start / PAGE_SIZE;			\
+	XA_STATE(xas, i->xarray, index);			\
+								\
+	len = PAGE_SIZE - offset_in_page(start);		\
+	rcu_read_lock();					\
+	xas_for_each(&xas, folio, ULONG_MAX) {			\
+		unsigned left;					\
+		size_t offset;					\
+		if (xas_retry(&xas, folio))			\
+			continue;				\
+		if (WARN_ON(xa_is_value(folio)))		\
+			break;					\
+		if (WARN_ON(folio_test_hugetlb(folio)))		\
+			break;					\
+		offset = offset_in_folio(folio, start + __off);	\
+		while (offset < folio_size(folio)) {		\
+			base = kmap_local_folio(folio, offset);	\
+			len = min(n, len);			\
+			left = (STEP);				\
+			kunmap_local(base);			\
+			len -= left;				\
+			__off += len;				\
+			n -= len;				\
+			if (left || n == 0)			\
+				goto __out;			\
+			offset += len;				\
+			len = PAGE_SIZE;			\
+		}						\
+	}							\
+__out:								\
+	rcu_read_unlock();					\
+	i->iov_offset += __off;					\
+	n = __off;						\
+}
+
+#define __iterate_and_advance(i, n, base, len, off, I, K) {	\
+	if (unlikely(i->count < n))				\
+		n = i->count;					\
+	if (likely(n)) {					\
+		if (likely(iter_is_ubuf(i))) {			\
+			void __user *base;			\
+			size_t len;				\
+			iterate_buf(i, n, base, len, off,	\
+						i->ubuf, (I)) 	\
+		} else if (likely(iter_is_iovec(i))) {		\
+			const struct iovec *iov = i->iov;	\
+			void __user *base;			\
+			size_t len;				\
+			iterate_iovec(i, n, base, len, off,	\
+						iov, (I))	\
+			i->nr_segs -= iov - i->iov;		\
+			i->iov = iov;				\
+		} else if (iov_iter_is_bvec(i)) {		\
+			const struct bio_vec *bvec = i->bvec;	\
+			void *base;				\
+			size_t len;				\
+			iterate_bvec(i, n, base, len, off,	\
+						bvec, (K))	\
+			i->nr_segs -= bvec - i->bvec;		\
+			i->bvec = bvec;				\
+		} else if (iov_iter_is_kvec(i)) {		\
+			const struct kvec *kvec = i->kvec;	\
+			void *base;				\
+			size_t len;				\
+			iterate_iovec(i, n, base, len, off,	\
+						kvec, (K))	\
+			i->nr_segs -= kvec - i->kvec;		\
+			i->kvec = kvec;				\
+		} else if (iov_iter_is_xarray(i)) {		\
+			void *base;				\
+			size_t len;				\
+			iterate_xarray(i, n, base, len, off,	\
+							(K))	\
+		}						\
+		i->count -= n;					\
+	}							\
+}
+#define iterate_and_advance(i, n, base, len, off, I, K) \
+	__iterate_and_advance(i, n, base, len, off, I, ((void)(K),0))
+
+static int copyout(void __user *to, const void *from, size_t n)
+{
+	if (should_fail_usercopy())
+		return n;
+	if (access_ok(to, n)) {
+		instrument_copy_to_user(to, from, n);
+		n = raw_copy_to_user(to, from, n);
+	}
+	return n;
+}
+
+static int copyin(void *to, const void __user *from, size_t n)
+{
+	size_t res = n;
+
+	if (should_fail_usercopy())
+		return n;
+	if (access_ok(from, n)) {
+		instrument_copy_from_user_before(to, from, n);
+		res = raw_copy_from_user(to, from, n);
+		instrument_copy_from_user_after(to, from, n, res);
+	}
+	return res;
+}
+
+static inline struct pipe_buffer *pipe_buf(const struct pipe_inode_info *pipe,
+					   unsigned int slot)
+{
+	return &pipe->bufs[slot & (pipe->ring_size - 1)];
+}
+
+#ifdef PIPE_PARANOIA
+static bool sanity(const struct iov_iter *i)
+{
+	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_head = pipe->head;
+	unsigned int p_tail = pipe->tail;
+	unsigned int p_occupancy = pipe_occupancy(p_head, p_tail);
+	unsigned int i_head = i->head;
+	unsigned int idx;
+
+	if (i->last_offset) {
+		struct pipe_buffer *p;
+		if (unlikely(p_occupancy == 0))
+			goto Bad;	// pipe must be non-empty
+		if (unlikely(i_head != p_head - 1))
+			goto Bad;	// must be at the last buffer...
+
+		p = pipe_buf(pipe, i_head);
+		if (unlikely(p->offset + p->len != abs(i->last_offset)))
+			goto Bad;	// ... at the end of segment
+	} else {
+		if (i_head != p_head)
+			goto Bad;	// must be right after the last buffer
+	}
+	return true;
+Bad:
+	printk(KERN_ERR "idx = %d, offset = %d\n", i_head, i->last_offset);
+	printk(KERN_ERR "head = %d, tail = %d, buffers = %d\n",
+			p_head, p_tail, pipe->ring_size);
+	for (idx = 0; idx < pipe->ring_size; idx++)
+		printk(KERN_ERR "[%p %p %d %d]\n",
+			pipe->bufs[idx].ops,
+			pipe->bufs[idx].page,
+			pipe->bufs[idx].offset,
+			pipe->bufs[idx].len);
+	WARN_ON(1);
+	return false;
+}
+#else
+#define sanity(i) true
+#endif
+
+static struct page *push_anon(struct pipe_inode_info *pipe, unsigned size)
+{
+	struct page *page = alloc_page(GFP_USER);
+	if (page) {
+		struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
+		*buf = (struct pipe_buffer) {
+			.ops = &default_pipe_buf_ops,
+			.page = page,
+			.offset = 0,
+			.len = size
+		};
+	}
+	return page;
+}
+
+static void push_page(struct pipe_inode_info *pipe, struct page *page,
+			unsigned int offset, unsigned int size)
+{
+	struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
+	*buf = (struct pipe_buffer) {
+		.ops = &page_cache_pipe_buf_ops,
+		.page = page,
+		.offset = offset,
+		.len = size
+	};
+	get_page(page);
+}
+
+static inline int last_offset(const struct pipe_buffer *buf)
+{
+	if (buf->ops == &default_pipe_buf_ops)
+		return buf->len;	// buf->offset is 0 for those
+	else
+		return -(buf->offset + buf->len);
+}
+
+static struct page *append_pipe(struct iov_iter *i, size_t size,
+				unsigned int *off)
+{
+	struct pipe_inode_info *pipe = i->pipe;
+	int offset = i->last_offset;
+	struct pipe_buffer *buf;
+	struct page *page;
+
+	if (offset > 0 && offset < PAGE_SIZE) {
+		// some space in the last buffer; add to it
+		buf = pipe_buf(pipe, pipe->head - 1);
+		size = min_t(size_t, size, PAGE_SIZE - offset);
+		buf->len += size;
+		i->last_offset += size;
+		i->count -= size;
+		*off = offset;
+		return buf->page;
+	}
+	// OK, we need a new buffer
+	*off = 0;
+	size = min_t(size_t, size, PAGE_SIZE);
+	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+		return NULL;
+	page = push_anon(pipe, size);
+	if (!page)
+		return NULL;
+	i->head = pipe->head - 1;
+	i->last_offset = size;
+	i->count -= size;
+	return page;
+}
+
+static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
+			 struct iov_iter *i)
+{
+	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int head = pipe->head;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+
+	if (unlikely(!bytes))
+		return 0;
+
+	if (!sanity(i))
+		return 0;
+
+	if (offset && i->last_offset == -offset) { // could we merge it?
+		struct pipe_buffer *buf = pipe_buf(pipe, head - 1);
+		if (buf->page == page) {
+			buf->len += bytes;
+			i->last_offset -= bytes;
+			i->count -= bytes;
+			return bytes;
+		}
+	}
+	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+		return 0;
+
+	push_page(pipe, page, offset, bytes);
+	i->last_offset = -(offset + bytes);
+	i->head = head;
+	i->count -= bytes;
+	return bytes;
+}
+
+/*
+ * fault_in_iov_iter_readable - fault in iov iterator for reading
+ * @i: iterator
+ * @size: maximum length
+ *
+ * Fault in one or more iovecs of the given iov_iter, to a maximum length of
+ * @size.  For each iovec, fault in each page that constitutes the iovec.
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ *
+ * Always returns 0 for non-userspace iterators.
+ */
+size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size)
+{
+	if (iter_is_ubuf(i)) {
+		size_t n = min(size, iov_iter_count(i));
+		n -= fault_in_readable(i->ubuf + i->iov_offset, n);
+		return size - n;
+	} else if (iter_is_iovec(i)) {
+		size_t count = min(size, iov_iter_count(i));
+		const struct iovec *p;
+		size_t skip;
+
+		size -= count;
+		for (p = i->iov, skip = i->iov_offset; count; p++, skip = 0) {
+			size_t len = min(count, p->iov_len - skip);
+			size_t ret;
+
+			if (unlikely(!len))
+				continue;
+			ret = fault_in_readable(p->iov_base + skip, len);
+			count -= len - ret;
+			if (ret)
+				break;
+		}
+		return count + size;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(fault_in_iov_iter_readable);
+
+/*
+ * fault_in_iov_iter_writeable - fault in iov iterator for writing
+ * @i: iterator
+ * @size: maximum length
+ *
+ * Faults in the iterator using get_user_pages(), i.e., without triggering
+ * hardware page faults.  This is primarily useful when we already know that
+ * some or all of the pages in @i aren't in memory.
+ *
+ * Returns the number of bytes not faulted in, like copy_to_user() and
+ * copy_from_user().
+ *
+ * Always returns 0 for non-user-space iterators.
+ */
+size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size)
+{
+	if (iter_is_ubuf(i)) {
+		size_t n = min(size, iov_iter_count(i));
+		n -= fault_in_safe_writeable(i->ubuf + i->iov_offset, n);
+		return size - n;
+	} else if (iter_is_iovec(i)) {
+		size_t count = min(size, iov_iter_count(i));
+		const struct iovec *p;
+		size_t skip;
+
+		size -= count;
+		for (p = i->iov, skip = i->iov_offset; count; p++, skip = 0) {
+			size_t len = min(count, p->iov_len - skip);
+			size_t ret;
+
+			if (unlikely(!len))
+				continue;
+			ret = fault_in_safe_writeable(p->iov_base + skip, len);
+			count -= len - ret;
+			if (ret)
+				break;
+		}
+		return count + size;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(fault_in_iov_iter_writeable);
+
+void iov_iter_init(struct iov_iter *i, unsigned int direction,
+			const struct iovec *iov, unsigned long nr_segs,
+			size_t count)
+{
+	WARN_ON(direction & ~(READ | WRITE));
+	*i = (struct iov_iter) {
+		.iter_type = ITER_IOVEC,
+		.nofault = false,
+		.user_backed = true,
+		.data_source = direction,
+		.iov = iov,
+		.nr_segs = nr_segs,
+		.iov_offset = 0,
+		.count = count
+	};
+}
+EXPORT_SYMBOL(iov_iter_init);
+
+// returns the offset in partial buffer (if any)
+static inline unsigned int pipe_npages(const struct iov_iter *i, int *npages)
+{
+	struct pipe_inode_info *pipe = i->pipe;
+	int used = pipe->head - pipe->tail;
+	int off = i->last_offset;
+
+	*npages = max((int)pipe->max_usage - used, 0);
+
+	if (off > 0 && off < PAGE_SIZE) { // anon and not full
+		(*npages)++;
+		return off;
+	}
+	return 0;
+}
+
+static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
+				struct iov_iter *i)
+{
+	unsigned int off, chunk;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+	if (unlikely(!bytes))
+		return 0;
+
+	if (!sanity(i))
+		return 0;
+
+	for (size_t n = bytes; n; n -= chunk) {
+		struct page *page = append_pipe(i, n, &off);
+		chunk = min_t(size_t, n, PAGE_SIZE - off);
+		if (!page)
+			return bytes - n;
+		memcpy_to_page(page, off, addr, chunk);
+		addr += chunk;
+	}
+	return bytes;
+}
+
+static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
+			      __wsum sum, size_t off)
+{
+	__wsum next = csum_partial_copy_nocheck(from, to, len);
+	return csum_block_add(sum, next, off);
+}
+
+static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
+					 struct iov_iter *i, __wsum *sump)
+{
+	__wsum sum = *sump;
+	size_t off = 0;
+	unsigned int chunk, r;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+	if (unlikely(!bytes))
+		return 0;
+
+	if (!sanity(i))
+		return 0;
+
+	while (bytes) {
+		struct page *page = append_pipe(i, bytes, &r);
+		char *p;
+
+		if (!page)
+			break;
+		chunk = min_t(size_t, bytes, PAGE_SIZE - r);
+		p = kmap_local_page(page);
+		sum = csum_and_memcpy(p + r, addr + off, chunk, sum, off);
+		kunmap_local(p);
+		off += chunk;
+		bytes -= chunk;
+	}
+	*sump = sum;
+	return off;
+}
+
+size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i)))
+		return copy_pipe_to_iter(addr, bytes, i);
+	if (user_backed_iter(i))
+		might_fault();
+	iterate_and_advance(i, bytes, base, len, off,
+		copyout(base, addr + off, len),
+		memcpy(base, addr + off, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL(_copy_to_iter);
+
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+static int copyout_mc(void __user *to, const void *from, size_t n)
+{
+	if (access_ok(to, n)) {
+		instrument_copy_to_user(to, from, n);
+		n = copy_mc_to_user((__force void *) to, from, n);
+	}
+	return n;
+}
+
+static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
+				struct iov_iter *i)
+{
+	size_t xfer = 0;
+	unsigned int off, chunk;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+	if (unlikely(!bytes))
+		return 0;
+
+	if (!sanity(i))
+		return 0;
+
+	while (bytes) {
+		struct page *page = append_pipe(i, bytes, &off);
+		unsigned long rem;
+		char *p;
+
+		if (!page)
+			break;
+		chunk = min_t(size_t, bytes, PAGE_SIZE - off);
+		p = kmap_local_page(page);
+		rem = copy_mc_to_kernel(p + off, addr + xfer, chunk);
+		chunk -= rem;
+		kunmap_local(p);
+		xfer += chunk;
+		bytes -= chunk;
+		if (rem) {
+			iov_iter_revert(i, rem);
+			break;
+		}
+	}
+	return xfer;
+}
+
+/**
+ * _copy_mc_to_iter - copy to iter with source memory error exception handling
+ * @addr: source kernel address
+ * @bytes: total transfer length
+ * @i: destination iterator
+ *
+ * The pmem driver deploys this for the dax operation
+ * (dax_copy_to_iter()) for dax reads (bypass page-cache and the
+ * block-layer). Upon #MC read(2) aborts and returns EIO or the bytes
+ * successfully copied.
+ *
+ * The main differences between this and typical _copy_to_iter().
+ *
+ * * Typical tail/residue handling after a fault retries the copy
+ *   byte-by-byte until the fault happens again. Re-triggering machine
+ *   checks is potentially fatal so the implementation uses source
+ *   alignment and poison alignment assumptions to avoid re-triggering
+ *   hardware exceptions.
+ *
+ * * ITER_KVEC, ITER_PIPE, and ITER_BVEC can return short copies.
+ *   Compare to copy_to_iter() where only ITER_IOVEC attempts might return
+ *   a short copy.
+ *
+ * Return: number of bytes copied (may be %0)
+ */
+size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i)))
+		return copy_mc_pipe_to_iter(addr, bytes, i);
+	if (user_backed_iter(i))
+		might_fault();
+	__iterate_and_advance(i, bytes, base, len, off,
+		copyout_mc(base, addr + off, len),
+		copy_mc_to_kernel(base, addr + off, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
+#endif /* CONFIG_ARCH_HAS_COPY_MC */
+
+size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i))) {
+		WARN_ON(1);
+		return 0;
+	}
+	if (user_backed_iter(i))
+		might_fault();
+	iterate_and_advance(i, bytes, base, len, off,
+		copyin(addr + off, base, len),
+		memcpy(addr + off, base, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL(_copy_from_iter);
+
+size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i))) {
+		WARN_ON(1);
+		return 0;
+	}
+	iterate_and_advance(i, bytes, base, len, off,
+		__copy_from_user_inatomic_nocache(addr + off, base, len),
+		memcpy(addr + off, base, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL(_copy_from_iter_nocache);
+
+#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+/**
+ * _copy_from_iter_flushcache - write destination through cpu cache
+ * @addr: destination kernel address
+ * @bytes: total transfer length
+ * @i: source iterator
+ *
+ * The pmem driver arranges for filesystem-dax to use this facility via
+ * dax_copy_from_iter() for ensuring that writes to persistent memory
+ * are flushed through the CPU cache. It is differentiated from
+ * _copy_from_iter_nocache() in that guarantees all data is flushed for
+ * all iterator types. The _copy_from_iter_nocache() only attempts to
+ * bypass the cache for the ITER_IOVEC case, and on some archs may use
+ * instructions that strand dirty-data in the cache.
+ *
+ * Return: number of bytes copied (may be %0)
+ */
+size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i))) {
+		WARN_ON(1);
+		return 0;
+	}
+	iterate_and_advance(i, bytes, base, len, off,
+		__copy_from_user_flushcache(addr + off, base, len),
+		memcpy_flushcache(addr + off, base, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);
+#endif
+
+static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
+{
+	struct page *head;
+	size_t v = n + offset;
+
+	/*
+	 * The general case needs to access the page order in order
+	 * to compute the page size.
+	 * However, we mostly deal with order-0 pages and thus can
+	 * avoid a possible cache line miss for requests that fit all
+	 * page orders.
+	 */
+	if (n <= v && v <= PAGE_SIZE)
+		return true;
+
+	head = compound_head(page);
+	v += (page - head) << PAGE_SHIFT;
+
+	if (likely(n <= v && v <= (page_size(head))))
+		return true;
+	WARN_ON(1);
+	return false;
+}
+
+size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
+			 struct iov_iter *i)
+{
+	size_t res = 0;
+	if (unlikely(!page_copy_sane(page, offset, bytes)))
+		return 0;
+	if (unlikely(iov_iter_is_pipe(i)))
+		return copy_page_to_iter_pipe(page, offset, bytes, i);
+	page += offset / PAGE_SIZE; // first subpage
+	offset %= PAGE_SIZE;
+	while (1) {
+		void *kaddr = kmap_local_page(page);
+		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
+		n = _copy_to_iter(kaddr + offset, n, i);
+		kunmap_local(kaddr);
+		res += n;
+		bytes -= n;
+		if (!bytes || !n)
+			break;
+		offset += n;
+		if (offset == PAGE_SIZE) {
+			page++;
+			offset = 0;
+		}
+	}
+	return res;
+}
+EXPORT_SYMBOL(copy_page_to_iter);
+
+size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
+			 struct iov_iter *i)
+{
+	size_t res = 0;
+	if (!page_copy_sane(page, offset, bytes))
+		return 0;
+	page += offset / PAGE_SIZE; // first subpage
+	offset %= PAGE_SIZE;
+	while (1) {
+		void *kaddr = kmap_local_page(page);
+		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
+		n = _copy_from_iter(kaddr + offset, n, i);
+		kunmap_local(kaddr);
+		res += n;
+		bytes -= n;
+		if (!bytes || !n)
+			break;
+		offset += n;
+		if (offset == PAGE_SIZE) {
+			page++;
+			offset = 0;
+		}
+	}
+	return res;
+}
+EXPORT_SYMBOL(copy_page_from_iter);
+
+static size_t pipe_zero(size_t bytes, struct iov_iter *i)
+{
+	unsigned int chunk, off;
+
+	if (unlikely(bytes > i->count))
+		bytes = i->count;
+	if (unlikely(!bytes))
+		return 0;
+
+	if (!sanity(i))
+		return 0;
+
+	for (size_t n = bytes; n; n -= chunk) {
+		struct page *page = append_pipe(i, n, &off);
+		char *p;
+
+		if (!page)
+			return bytes - n;
+		chunk = min_t(size_t, n, PAGE_SIZE - off);
+		p = kmap_local_page(page);
+		memset(p + off, 0, chunk);
+		kunmap_local(p);
+	}
+	return bytes;
+}
+
+size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
+{
+	if (unlikely(iov_iter_is_pipe(i)))
+		return pipe_zero(bytes, i);
+	iterate_and_advance(i, bytes, base, len, count,
+		clear_user(base, len),
+		memset(base, 0, len)
+	)
+
+	return bytes;
+}
+EXPORT_SYMBOL(iov_iter_zero);
+
+size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t bytes,
+				  struct iov_iter *i)
+{
+	char *kaddr = kmap_atomic(page), *p = kaddr + offset;
+	if (unlikely(!page_copy_sane(page, offset, bytes))) {
+		kunmap_atomic(kaddr);
+		return 0;
+	}
+	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
+		kunmap_atomic(kaddr);
+		WARN_ON(1);
+		return 0;
+	}
+	iterate_and_advance(i, bytes, base, len, off,
+		copyin(p + off, base, len),
+		memcpy(p + off, base, len)
+	)
+	kunmap_atomic(kaddr);
+	return bytes;
+}
+EXPORT_SYMBOL(copy_page_from_iter_atomic);
+
+static void pipe_advance(struct iov_iter *i, size_t size)
+{
+	struct pipe_inode_info *pipe = i->pipe;
+	int off = i->last_offset;
+
+	if (!off && !size) {
+		pipe_discard_from(pipe, i->start_head); // discard everything
+		return;
+	}
+	i->count -= size;
+	while (1) {
+		struct pipe_buffer *buf = pipe_buf(pipe, i->head);
+		if (off) /* make it relative to the beginning of buffer */
+			size += abs(off) - buf->offset;
+		if (size <= buf->len) {
+			buf->len = size;
+			i->last_offset = last_offset(buf);
+			break;
+		}
+		size -= buf->len;
+		i->head++;
+		off = 0;
+	}
+	pipe_discard_from(pipe, i->head + 1); // discard everything past this one
+}
+
+static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
+{
+	const struct bio_vec *bvec, *end;
+
+	if (!i->count)
+		return;
+	i->count -= size;
+
+	size += i->iov_offset;
+
+	for (bvec = i->bvec, end = bvec + i->nr_segs; bvec < end; bvec++) {
+		if (likely(size < bvec->bv_len))
+			break;
+		size -= bvec->bv_len;
+	}
+	i->iov_offset = size;
+	i->nr_segs -= bvec - i->bvec;
+	i->bvec = bvec;
+}
+
+static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
+{
+	const struct iovec *iov, *end;
+
+	if (!i->count)
+		return;
+	i->count -= size;
+
+	size += i->iov_offset; // from beginning of current segment
+	for (iov = i->iov, end = iov + i->nr_segs; iov < end; iov++) {
+		if (likely(size < iov->iov_len))
+			break;
+		size -= iov->iov_len;
+	}
+	i->iov_offset = size;
+	i->nr_segs -= iov - i->iov;
+	i->iov = iov;
+}
+
+void iov_iter_advance(struct iov_iter *i, size_t size)
+{
+	if (unlikely(i->count < size))
+		size = i->count;
+	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
+		i->iov_offset += size;
+		i->count -= size;
+	} else if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
+		/* iovec and kvec have identical layouts */
+		iov_iter_iovec_advance(i, size);
+	} else if (iov_iter_is_bvec(i)) {
+		iov_iter_bvec_advance(i, size);
+	} else if (iov_iter_is_pipe(i)) {
+		pipe_advance(i, size);
+	} else if (iov_iter_is_discard(i)) {
+		i->count -= size;
+	}
+}
+EXPORT_SYMBOL(iov_iter_advance);
+
+void iov_iter_revert(struct iov_iter *i, size_t unroll)
+{
+	if (!unroll)
+		return;
+	if (WARN_ON(unroll > MAX_RW_COUNT))
+		return;
+	i->count += unroll;
+	if (unlikely(iov_iter_is_pipe(i))) {
+		struct pipe_inode_info *pipe = i->pipe;
+		unsigned int head = pipe->head;
+
+		while (head > i->start_head) {
+			struct pipe_buffer *b = pipe_buf(pipe, --head);
+			if (unroll < b->len) {
+				b->len -= unroll;
+				i->last_offset = last_offset(b);
+				i->head = head;
+				return;
+			}
+			unroll -= b->len;
+			pipe_buf_release(pipe, b);
+			pipe->head--;
+		}
+		i->last_offset = 0;
+		i->head = head;
+		return;
+	}
+	if (unlikely(iov_iter_is_discard(i)))
+		return;
+	if (unroll <= i->iov_offset) {
+		i->iov_offset -= unroll;
+		return;
+	}
+	unroll -= i->iov_offset;
+	if (iov_iter_is_xarray(i) || iter_is_ubuf(i)) {
+		BUG(); /* We should never go beyond the start of the specified
+			* range since we might then be straying into pages that
+			* aren't pinned.
+			*/
+	} else if (iov_iter_is_bvec(i)) {
+		const struct bio_vec *bvec = i->bvec;
+		while (1) {
+			size_t n = (--bvec)->bv_len;
+			i->nr_segs++;
+			if (unroll <= n) {
+				i->bvec = bvec;
+				i->iov_offset = n - unroll;
+				return;
+			}
+			unroll -= n;
+		}
+	} else { /* same logics for iovec and kvec */
+		const struct iovec *iov = i->iov;
+		while (1) {
+			size_t n = (--iov)->iov_len;
+			i->nr_segs++;
+			if (unroll <= n) {
+				i->iov = iov;
+				i->iov_offset = n - unroll;
+				return;
+			}
+			unroll -= n;
+		}
+	}
+}
+EXPORT_SYMBOL(iov_iter_revert);
+
+/*
+ * Return the count of just the current iov_iter segment.
+ */
+size_t iov_iter_single_seg_count(const struct iov_iter *i)
+{
+	if (i->nr_segs > 1) {
+		if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
+			return min(i->count, i->iov->iov_len - i->iov_offset);
+		if (iov_iter_is_bvec(i))
+			return min(i->count, i->bvec->bv_len - i->iov_offset);
+	}
+	return i->count;
+}
+EXPORT_SYMBOL(iov_iter_single_seg_count);
+
+void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
+			const struct kvec *kvec, unsigned long nr_segs,
+			size_t count)
+{
+	WARN_ON(direction & ~(READ | WRITE));
+	*i = (struct iov_iter){
+		.iter_type = ITER_KVEC,
+		.data_source = direction,
+		.kvec = kvec,
+		.nr_segs = nr_segs,
+		.iov_offset = 0,
+		.count = count
+	};
+}
+EXPORT_SYMBOL(iov_iter_kvec);
+
+void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
+			const struct bio_vec *bvec, unsigned long nr_segs,
+			size_t count)
+{
+	WARN_ON(direction & ~(READ | WRITE));
+	*i = (struct iov_iter){
+		.iter_type = ITER_BVEC,
+		.data_source = direction,
+		.bvec = bvec,
+		.nr_segs = nr_segs,
+		.iov_offset = 0,
+		.count = count
+	};
+}
+EXPORT_SYMBOL(iov_iter_bvec);
+
+void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
+			struct pipe_inode_info *pipe,
+			size_t count)
+{
+	BUG_ON(direction != READ);
+	WARN_ON(pipe_full(pipe->head, pipe->tail, pipe->ring_size));
+	*i = (struct iov_iter){
+		.iter_type = ITER_PIPE,
+		.data_source = false,
+		.pipe = pipe,
+		.head = pipe->head,
+		.start_head = pipe->head,
+		.last_offset = 0,
+		.count = count
+	};
+}
+EXPORT_SYMBOL(iov_iter_pipe);
+
+/**
+ * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
+ * @i: The iterator to initialise.
+ * @direction: The direction of the transfer.
+ * @xarray: The xarray to access.
+ * @start: The start file position.
+ * @count: The size of the I/O buffer in bytes.
+ *
+ * Set up an I/O iterator to either draw data out of the pages attached to an
+ * inode or to inject data into those pages.  The pages *must* be prevented
+ * from evaporation, either by taking a ref on them or locking them by the
+ * caller.
+ */
+void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
+		     struct xarray *xarray, loff_t start, size_t count)
+{
+	BUG_ON(direction & ~1);
+	*i = (struct iov_iter) {
+		.iter_type = ITER_XARRAY,
+		.data_source = direction,
+		.xarray = xarray,
+		.xarray_start = start,
+		.count = count,
+		.iov_offset = 0
+	};
+}
+EXPORT_SYMBOL(iov_iter_xarray);
+
+/**
+ * iov_iter_discard - Initialise an I/O iterator that discards data
+ * @i: The iterator to initialise.
+ * @direction: The direction of the transfer.
+ * @count: The size of the I/O buffer in bytes.
+ *
+ * Set up an I/O iterator that just discards everything that's written to it.
+ * It's only available as a READ iterator.
+ */
+void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
+{
+	BUG_ON(direction != READ);
+	*i = (struct iov_iter){
+		.iter_type = ITER_DISCARD,
+		.data_source = false,
+		.count = count,
+		.iov_offset = 0
+	};
+}
+EXPORT_SYMBOL(iov_iter_discard);
+
+static bool iov_iter_aligned_iovec(const struct iov_iter *i, unsigned addr_mask,
+				   unsigned len_mask)
+{
+	size_t size = i->count;
+	size_t skip = i->iov_offset;
+	unsigned k;
+
+	for (k = 0; k < i->nr_segs; k++, skip = 0) {
+		size_t len = i->iov[k].iov_len - skip;
+
+		if (len > size)
+			len = size;
+		if (len & len_mask)
+			return false;
+		if ((unsigned long)(i->iov[k].iov_base + skip) & addr_mask)
+			return false;
+
+		size -= len;
+		if (!size)
+			break;
+	}
+	return true;
+}
+
+static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask,
+				  unsigned len_mask)
+{
+	size_t size = i->count;
+	unsigned skip = i->iov_offset;
+	unsigned k;
+
+	for (k = 0; k < i->nr_segs; k++, skip = 0) {
+		size_t len = i->bvec[k].bv_len - skip;
+
+		if (len > size)
+			len = size;
+		if (len & len_mask)
+			return false;
+		if ((unsigned long)(i->bvec[k].bv_offset + skip) & addr_mask)
+			return false;
+
+		size -= len;
+		if (!size)
+			break;
+	}
+	return true;
+}
+
+/**
+ * iov_iter_is_aligned() - Check if the addresses and lengths of each segments
+ * 	are aligned to the parameters.
+ *
+ * @i: &struct iov_iter to restore
+ * @addr_mask: bit mask to check against the iov element's addresses
+ * @len_mask: bit mask to check against the iov element's lengths
+ *
+ * Return: false if any addresses or lengths intersect with the provided masks
+ */
+bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
+			 unsigned len_mask)
+{
+	if (likely(iter_is_ubuf(i))) {
+		if (i->count & len_mask)
+			return false;
+		if ((unsigned long)(i->ubuf + i->iov_offset) & addr_mask)
+			return false;
+		return true;
+	}
+
+	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
+		return iov_iter_aligned_iovec(i, addr_mask, len_mask);
+
+	if (iov_iter_is_bvec(i))
+		return iov_iter_aligned_bvec(i, addr_mask, len_mask);
+
+	if (iov_iter_is_pipe(i)) {
+		size_t size = i->count;
+
+		if (size & len_mask)
+			return false;
+		if (size && i->last_offset > 0) {
+			if (i->last_offset & addr_mask)
+				return false;
+		}
+
+		return true;
+	}
+
+	if (iov_iter_is_xarray(i)) {
+		if (i->count & len_mask)
+			return false;
+		if ((i->xarray_start + i->iov_offset) & addr_mask)
+			return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(iov_iter_is_aligned);
+
+static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
+{
+	unsigned long res = 0;
+	size_t size = i->count;
+	size_t skip = i->iov_offset;
+	unsigned k;
+
+	for (k = 0; k < i->nr_segs; k++, skip = 0) {
+		size_t len = i->iov[k].iov_len - skip;
+		if (len) {
+			res |= (unsigned long)i->iov[k].iov_base + skip;
+			if (len > size)
+				len = size;
+			res |= len;
+			size -= len;
+			if (!size)
+				break;
+		}
+	}
+	return res;
+}
+
+static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
+{
+	unsigned res = 0;
+	size_t size = i->count;
+	unsigned skip = i->iov_offset;
+	unsigned k;
+
+	for (k = 0; k < i->nr_segs; k++, skip = 0) {
+		size_t len = i->bvec[k].bv_len - skip;
+		res |= (unsigned long)i->bvec[k].bv_offset + skip;
+		if (len > size)
+			len = size;
+		res |= len;
+		size -= len;
+		if (!size)
+			break;
+	}
+	return res;
+}
+
+unsigned long iov_iter_alignment(const struct iov_iter *i)
+{
+	if (likely(iter_is_ubuf(i))) {
+		size_t size = i->count;
+		if (size)
+			return ((unsigned long)i->ubuf + i->iov_offset) | size;
+		return 0;
+	}
+
+	/* iovec and kvec have identical layouts */
+	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
+		return iov_iter_alignment_iovec(i);
+
+	if (iov_iter_is_bvec(i))
+		return iov_iter_alignment_bvec(i);
+
+	if (iov_iter_is_pipe(i)) {
+		size_t size = i->count;
+
+		if (size && i->last_offset > 0)
+			return size | i->last_offset;
+		return size;
+	}
+
+	if (iov_iter_is_xarray(i))
+		return (i->xarray_start + i->iov_offset) | i->count;
+
+	return 0;
+}
+EXPORT_SYMBOL(iov_iter_alignment);
+
+unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
+{
+	unsigned long res = 0;
+	unsigned long v = 0;
+	size_t size = i->count;
+	unsigned k;
+
+	if (iter_is_ubuf(i))
+		return 0;
+
+	if (WARN_ON(!iter_is_iovec(i)))
+		return ~0U;
+
+	for (k = 0; k < i->nr_segs; k++) {
+		if (i->iov[k].iov_len) {
+			unsigned long base = (unsigned long)i->iov[k].iov_base;
+			if (v) // if not the first one
+				res |= base | v; // this start | previous end
+			v = base + i->iov[k].iov_len;
+			if (size <= i->iov[k].iov_len)
+				break;
+			size -= i->iov[k].iov_len;
+		}
+	}
+	return res;
+}
+EXPORT_SYMBOL(iov_iter_gap_alignment);
+
+static int want_pages_array(struct page ***res, size_t size,
+			    size_t start, unsigned int maxpages)
+{
+	unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE);
+
+	if (count > maxpages)
+		count = maxpages;
+	WARN_ON(!count);	// caller should've prevented that
+	if (!*res) {
+		*res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
+		if (!*res)
+			return 0;
+	}
+	return count;
+}
+
+static ssize_t pipe_get_pages(struct iov_iter *i,
+		   struct page ***pages, size_t maxsize, unsigned maxpages,
+		   size_t *start)
+{
+	unsigned int npages, count, off, chunk;
+	struct page **p;
+	size_t left;
+
+	if (!sanity(i))
+		return -EFAULT;
+
+	*start = off = pipe_npages(i, &npages);
+	if (!npages)
+		return -EFAULT;
+	count = want_pages_array(pages, maxsize, off, min(npages, maxpages));
+	if (!count)
+		return -ENOMEM;
+	p = *pages;
+	for (npages = 0, left = maxsize ; npages < count; npages++, left -= chunk) {
+		struct page *page = append_pipe(i, left, &off);
+		if (!page)
+			break;
+		chunk = min_t(size_t, left, PAGE_SIZE - off);
+		get_page(*p++ = page);
+	}
+	if (!npages)
+		return -EFAULT;
+	return maxsize - left;
+}
+
+static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
+					  pgoff_t index, unsigned int nr_pages)
+{
+	XA_STATE(xas, xa, index);
+	struct page *page;
+	unsigned int ret = 0;
+
+	rcu_read_lock();
+	for (page = xas_load(&xas); page; page = xas_next(&xas)) {
+		if (xas_retry(&xas, page))
+			continue;
+
+		/* Has the page moved or been split? */
+		if (unlikely(page != xas_reload(&xas))) {
+			xas_reset(&xas);
+			continue;
+		}
+
+		pages[ret] = find_subpage(page, xas.xa_index);
+		get_page(pages[ret]);
+		if (++ret == nr_pages)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+static ssize_t iter_xarray_get_pages(struct iov_iter *i,
+				     struct page ***pages, size_t maxsize,
+				     unsigned maxpages, size_t *_start_offset)
+{
+	unsigned nr, offset, count;
+	pgoff_t index;
+	loff_t pos;
+
+	pos = i->xarray_start + i->iov_offset;
+	index = pos >> PAGE_SHIFT;
+	offset = pos & ~PAGE_MASK;
+	*_start_offset = offset;
+
+	count = want_pages_array(pages, maxsize, offset, maxpages);
+	if (!count)
+		return -ENOMEM;
+	nr = iter_xarray_populate_pages(*pages, i->xarray, index, count);
+	if (nr == 0)
+		return 0;
+
+	maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
+	i->iov_offset += maxsize;
+	i->count -= maxsize;
+	return maxsize;
+}
+
+/* must be done on non-empty ITER_UBUF or ITER_IOVEC one */
+static unsigned long first_iovec_segment(const struct iov_iter *i, size_t *size)
+{
+	size_t skip;
+	long k;
+
+	if (iter_is_ubuf(i))
+		return (unsigned long)i->ubuf + i->iov_offset;
+
+	for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) {
+		size_t len = i->iov[k].iov_len - skip;
+
+		if (unlikely(!len))
+			continue;
+		if (*size > len)
+			*size = len;
+		return (unsigned long)i->iov[k].iov_base + skip;
+	}
+	BUG(); // if it had been empty, we wouldn't get called
+}
+
+/* must be done on non-empty ITER_BVEC one */
+static struct page *first_bvec_segment(const struct iov_iter *i,
+				       size_t *size, size_t *start)
+{
+	struct page *page;
+	size_t skip = i->iov_offset, len;
+
+	len = i->bvec->bv_len - skip;
+	if (*size > len)
+		*size = len;
+	skip += i->bvec->bv_offset;
+	page = i->bvec->bv_page + skip / PAGE_SIZE;
+	*start = skip % PAGE_SIZE;
+	return page;
+}
+
+static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
+		   struct page ***pages, size_t maxsize,
+		   unsigned int maxpages, size_t *start)
+{
+	unsigned int n;
+
+	if (maxsize > i->count)
+		maxsize = i->count;
+	if (!maxsize)
+		return 0;
+	if (maxsize > MAX_RW_COUNT)
+		maxsize = MAX_RW_COUNT;
+
+	if (likely(user_backed_iter(i))) {
+		unsigned int gup_flags = 0;
+		unsigned long addr;
+		int res;
+
+		if (iov_iter_rw(i) != WRITE)
+			gup_flags |= FOLL_WRITE;
+		if (i->nofault)
+			gup_flags |= FOLL_NOFAULT;
+
+		addr = first_iovec_segment(i, &maxsize);
+		*start = addr % PAGE_SIZE;
+		addr &= PAGE_MASK;
+		n = want_pages_array(pages, maxsize, *start, maxpages);
+		if (!n)
+			return -ENOMEM;
+		res = get_user_pages_fast(addr, n, gup_flags, *pages);
+		if (unlikely(res <= 0))
+			return res;
+		maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - *start);
+		iov_iter_advance(i, maxsize);
+		return maxsize;
+	}
+	if (iov_iter_is_bvec(i)) {
+		struct page **p;
+		struct page *page;
+
+		page = first_bvec_segment(i, &maxsize, start);
+		n = want_pages_array(pages, maxsize, *start, maxpages);
+		if (!n)
+			return -ENOMEM;
+		p = *pages;
+		for (int k = 0; k < n; k++)
+			get_page(p[k] = page + k);
+		maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
+		i->count -= maxsize;
+		i->iov_offset += maxsize;
+		if (i->iov_offset == i->bvec->bv_len) {
+			i->iov_offset = 0;
+			i->bvec++;
+			i->nr_segs--;
+		}
+		return maxsize;
+	}
+	if (iov_iter_is_pipe(i))
+		return pipe_get_pages(i, pages, maxsize, maxpages, start);
+	if (iov_iter_is_xarray(i))
+		return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
+	return -EFAULT;
+}
+
+ssize_t iov_iter_get_pages2(struct iov_iter *i,
+		   struct page **pages, size_t maxsize, unsigned maxpages,
+		   size_t *start)
+{
+	if (!maxpages)
+		return 0;
+	BUG_ON(!pages);
+
+	return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start);
+}
+EXPORT_SYMBOL(iov_iter_get_pages2);
+
+ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
+		   struct page ***pages, size_t maxsize,
+		   size_t *start)
+{
+	ssize_t len;
+
+	*pages = NULL;
+
+	len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start);
+	if (len <= 0) {
+		kvfree(*pages);
+		*pages = NULL;
+	}
+	return len;
+}
+EXPORT_SYMBOL(iov_iter_get_pages_alloc2);
+
+size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
+			       struct iov_iter *i)
+{
+	__wsum sum, next;
+	sum = *csum;
+	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
+		WARN_ON(1);
+		return 0;
+	}
+	iterate_and_advance(i, bytes, base, len, off, ({
+		next = csum_and_copy_from_user(base, addr + off, len);
+		sum = csum_block_add(sum, next, off);
+		next ? 0 : len;
+	}), ({
+		sum = csum_and_memcpy(addr + off, base, len, sum, off);
+	})
+	)
+	*csum = sum;
+	return bytes;
+}
+EXPORT_SYMBOL(csum_and_copy_from_iter);
+
+size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
+			     struct iov_iter *i)
+{
+	struct csum_state *csstate = _csstate;
+	__wsum sum, next;
+
+	if (unlikely(iov_iter_is_discard(i))) {
+		WARN_ON(1);	/* for now */
+		return 0;
+	}
+
+	sum = csum_shift(csstate->csum, csstate->off);
+	if (unlikely(iov_iter_is_pipe(i)))
+		bytes = csum_and_copy_to_pipe_iter(addr, bytes, i, &sum);
+	else iterate_and_advance(i, bytes, base, len, off, ({
+		next = csum_and_copy_to_user(addr + off, base, len);
+		sum = csum_block_add(sum, next, off);
+		next ? 0 : len;
+	}), ({
+		sum = csum_and_memcpy(base, addr + off, len, sum, off);
+	})
+	)
+	csstate->csum = csum_shift(sum, csstate->off);
+	csstate->off += bytes;
+	return bytes;
+}
+EXPORT_SYMBOL(csum_and_copy_to_iter);
+
+size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
+		struct iov_iter *i)
+{
+#ifdef CONFIG_CRYPTO_HASH
+	struct ahash_request *hash = hashp;
+	struct scatterlist sg;
+	size_t copied;
+
+	copied = copy_to_iter(addr, bytes, i);
+	sg_init_one(&sg, addr, copied);
+	ahash_request_set_crypt(hash, &sg, NULL, copied);
+	crypto_ahash_update(hash);
+	return copied;
+#else
+	return 0;
+#endif
+}
+EXPORT_SYMBOL(hash_and_copy_to_iter);
+
+static int iov_npages(const struct iov_iter *i, int maxpages)
+{
+	size_t skip = i->iov_offset, size = i->count;
+	const struct iovec *p;
+	int npages = 0;
+
+	for (p = i->iov; size; skip = 0, p++) {
+		unsigned offs = offset_in_page(p->iov_base + skip);
+		size_t len = min(p->iov_len - skip, size);
+
+		if (len) {
+			size -= len;
+			npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
+			if (unlikely(npages > maxpages))
+				return maxpages;
+		}
+	}
+	return npages;
+}
+
+static int bvec_npages(const struct iov_iter *i, int maxpages)
+{
+	size_t skip = i->iov_offset, size = i->count;
+	const struct bio_vec *p;
+	int npages = 0;
+
+	for (p = i->bvec; size; skip = 0, p++) {
+		unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
+		size_t len = min(p->bv_len - skip, size);
+
+		size -= len;
+		npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
+		if (unlikely(npages > maxpages))
+			return maxpages;
+	}
+	return npages;
+}
+
+int iov_iter_npages(const struct iov_iter *i, int maxpages)
+{
+	if (unlikely(!i->count))
+		return 0;
+	if (likely(iter_is_ubuf(i))) {
+		unsigned offs = offset_in_page(i->ubuf + i->iov_offset);
+		int npages = DIV_ROUND_UP(offs + i->count, PAGE_SIZE);
+		return min(npages, maxpages);
+	}
+	/* iovec and kvec have identical layouts */
+	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
+		return iov_npages(i, maxpages);
+	if (iov_iter_is_bvec(i))
+		return bvec_npages(i, maxpages);
+	if (iov_iter_is_pipe(i)) {
+		int npages;
+
+		if (!sanity(i))
+			return 0;
+
+		pipe_npages(i, &npages);
+		return min(npages, maxpages);
+	}
+	if (iov_iter_is_xarray(i)) {
+		unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
+		int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
+		return min(npages, maxpages);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(iov_iter_npages);
+
+const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
+{
+	*new = *old;
+	if (unlikely(iov_iter_is_pipe(new))) {
+		WARN_ON(1);
+		return NULL;
+	}
+	if (iov_iter_is_bvec(new))
+		return new->bvec = kmemdup(new->bvec,
+				    new->nr_segs * sizeof(struct bio_vec),
+				    flags);
+	else if (iov_iter_is_kvec(new) || iter_is_iovec(new))
+		/* iovec and kvec have identical layout */
+		return new->iov = kmemdup(new->iov,
+				   new->nr_segs * sizeof(struct iovec),
+				   flags);
+	return NULL;
+}
+EXPORT_SYMBOL(dup_iter);
+
+static int copy_compat_iovec_from_user(struct iovec *iov,
+		const struct iovec __user *uvec, unsigned long nr_segs)
+{
+	const struct compat_iovec __user *uiov =
+		(const struct compat_iovec __user *)uvec;
+	int ret = -EFAULT, i;
+
+	if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
+		return -EFAULT;
+
+	for (i = 0; i < nr_segs; i++) {
+		compat_uptr_t buf;
+		compat_ssize_t len;
+
+		unsafe_get_user(len, &uiov[i].iov_len, uaccess_end);
+		unsafe_get_user(buf, &uiov[i].iov_base, uaccess_end);
+
+		/* check for compat_size_t not fitting in compat_ssize_t .. */
+		if (len < 0) {
+			ret = -EINVAL;
+			goto uaccess_end;
+		}
+		iov[i].iov_base = compat_ptr(buf);
+		iov[i].iov_len = len;
+	}
+
+	ret = 0;
+uaccess_end:
+	user_access_end();
+	return ret;
+}
+
+static int copy_iovec_from_user(struct iovec *iov,
+		const struct iovec __user *uvec, unsigned long nr_segs)
+{
+	unsigned long seg;
+
+	if (copy_from_user(iov, uvec, nr_segs * sizeof(*uvec)))
+		return -EFAULT;
+	for (seg = 0; seg < nr_segs; seg++) {
+		if ((ssize_t)iov[seg].iov_len < 0)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+struct iovec *iovec_from_user(const struct iovec __user *uvec,
+		unsigned long nr_segs, unsigned long fast_segs,
+		struct iovec *fast_iov, bool compat)
+{
+	struct iovec *iov = fast_iov;
+	int ret;
+
+	/*
+	 * SuS says "The readv() function *may* fail if the iovcnt argument was
+	 * less than or equal to 0, or greater than {IOV_MAX}.  Linux has
+	 * traditionally returned zero for zero segments, so...
+	 */
+	if (nr_segs == 0)
+		return iov;
+	if (nr_segs > UIO_MAXIOV)
+		return ERR_PTR(-EINVAL);
+	if (nr_segs > fast_segs) {
+		iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
+		if (!iov)
+			return ERR_PTR(-ENOMEM);
+	}
+
+	if (compat)
+		ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
+	else
+		ret = copy_iovec_from_user(iov, uvec, nr_segs);
+	if (ret) {
+		if (iov != fast_iov)
+			kfree(iov);
+		return ERR_PTR(ret);
+	}
+
+	return iov;
+}
+
+ssize_t __import_iovec(int type, const struct iovec __user *uvec,
+		 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
+		 struct iov_iter *i, bool compat)
+{
+	ssize_t total_len = 0;
+	unsigned long seg;
+	struct iovec *iov;
+
+	iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
+	if (IS_ERR(iov)) {
+		*iovp = NULL;
+		return PTR_ERR(iov);
+	}
+
+	/*
+	 * According to the Single Unix Specification we should return EINVAL if
+	 * an element length is < 0 when cast to ssize_t or if the total length
+	 * would overflow the ssize_t return value of the system call.
+	 *
+	 * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
+	 * overflow case.
+	 */
+	for (seg = 0; seg < nr_segs; seg++) {
+		ssize_t len = (ssize_t)iov[seg].iov_len;
+
+		if (!access_ok(iov[seg].iov_base, len)) {
+			if (iov != *iovp)
+				kfree(iov);
+			*iovp = NULL;
+			return -EFAULT;
+		}
+
+		if (len > MAX_RW_COUNT - total_len) {
+			len = MAX_RW_COUNT - total_len;
+			iov[seg].iov_len = len;
+		}
+		total_len += len;
+	}
+
+	iov_iter_init(i, type, iov, nr_segs, total_len);
+	if (iov == *iovp)
+		*iovp = NULL;
+	else
+		*iovp = iov;
+	return total_len;
+}
+
+/**
+ * import_iovec() - Copy an array of &struct iovec from userspace
+ *     into the kernel, check that it is valid, and initialize a new
+ *     &struct iov_iter iterator to access it.
+ *
+ * @type: One of %READ or %WRITE.
+ * @uvec: Pointer to the userspace array.
+ * @nr_segs: Number of elements in userspace array.
+ * @fast_segs: Number of elements in @iov.
+ * @iovp: (input and output parameter) Pointer to pointer to (usually small
+ *     on-stack) kernel array.
+ * @i: Pointer to iterator that will be initialized on success.
+ *
+ * If the array pointed to by *@iov is large enough to hold all @nr_segs,
+ * then this function places %NULL in *@iov on return. Otherwise, a new
+ * array will be allocated and the result placed in *@iov. This means that
+ * the caller may call kfree() on *@iov regardless of whether the small
+ * on-stack array was used or not (and regardless of whether this function
+ * returns an error or not).
+ *
+ * Return: Negative error code on error, bytes imported on success
+ */
+ssize_t import_iovec(int type, const struct iovec __user *uvec,
+		 unsigned nr_segs, unsigned fast_segs,
+		 struct iovec **iovp, struct iov_iter *i)
+{
+	return __import_iovec(type, uvec, nr_segs, fast_segs, iovp, i,
+			      in_compat_syscall());
+}
+EXPORT_SYMBOL(import_iovec);
+
+int import_single_range(int rw, void __user *buf, size_t len,
+		 struct iovec *iov, struct iov_iter *i)
+{
+	if (len > MAX_RW_COUNT)
+		len = MAX_RW_COUNT;
+	if (unlikely(!access_ok(buf, len)))
+		return -EFAULT;
+
+	iov->iov_base = buf;
+	iov->iov_len = len;
+	iov_iter_init(i, rw, iov, 1, len);
+	return 0;
+}
+EXPORT_SYMBOL(import_single_range);
+
+/**
+ * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
+ *     iov_iter_save_state() was called.
+ *
+ * @i: &struct iov_iter to restore
+ * @state: state to restore from
+ *
+ * Used after iov_iter_save_state() to bring restore @i, if operations may
+ * have advanced it.
+ *
+ * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
+ */
+void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
+{
+	if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) &&
+			 !iov_iter_is_kvec(i) && !iter_is_ubuf(i))
+		return;
+	i->iov_offset = state->iov_offset;
+	i->count = state->count;
+	if (iter_is_ubuf(i))
+		return;
+	/*
+	 * For the *vec iters, nr_segs + iov is constant - if we increment
+	 * the vec, then we also decrement the nr_segs count. Hence we don't
+	 * need to track both of these, just one is enough and we can deduct
+	 * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
+	 * size, so we can just increment the iov pointer as they are unionzed.
+	 * ITER_BVEC _may_ be the same size on some archs, but on others it is
+	 * not. Be safe and handle it separately.
+	 */
+	BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
+	if (iov_iter_is_bvec(i))
+		i->bvec -= state->nr_segs - i->nr_segs;
+	else
+		i->iov -= state->nr_segs - i->nr_segs;
+	i->nr_segs = state->nr_segs;
+}