Commit 3337ab08 authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

iov_iter: Introduce nofault flag to disable page faults 



Introduce a new nofault flag to indicate to iov_iter_get_pages not to
fault in user pages.

This is implemented by passing the FOLL_NOFAULT flag to get_user_pages,
which causes get_user_pages to fail when it would otherwise fault in a
page. We'll use the ->nofault flag to prevent iomap_dio_rw from faulting
in pages when page faults are not allowed.

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent 55b8fe70

include/linux/uio.h

+1 −0
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ struct iov_iter_state { 


struct iov_iter {

	u8 iter_type;

	bool nofault;

	bool data_source;

	size_t iov_offset;

	size_t count;

lib/iov_iter.c

+15 −5
Original line number Diff line number Diff line
@@ -513,6 +513,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction, 
	WARN_ON(direction & ~(READ | WRITE));

	*i = (struct iov_iter) {

		.iter_type = ITER_IOVEC,

		.nofault = false,

		.data_source = direction,

		.iov = iov,

		.nr_segs = nr_segs,
@@ -1527,13 +1528,17 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, 
		return 0;



	if (likely(iter_is_iovec(i))) {

		unsigned int gup_flags = 0;

		unsigned long addr;



		if (iov_iter_rw(i) != WRITE)

			gup_flags |= FOLL_WRITE;

		if (i->nofault)

			gup_flags |= FOLL_NOFAULT;



		addr = first_iovec_segment(i, &len, start, maxsize, maxpages);

		n = DIV_ROUND_UP(len, PAGE_SIZE);

		res = get_user_pages_fast(addr, n,

				iov_iter_rw(i) != WRITE ?  FOLL_WRITE : 0,

				pages);

		res = get_user_pages_fast(addr, n, gup_flags, pages);

		if (unlikely(res <= 0))

			return res;

		return (res == n ? len : res * PAGE_SIZE) - *start;
@@ -1649,15 +1654,20 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, 
		return 0;



	if (likely(iter_is_iovec(i))) {

		unsigned int gup_flags = 0;

		unsigned long addr;



		if (iov_iter_rw(i) != WRITE)

			gup_flags |= FOLL_WRITE;

		if (i->nofault)

			gup_flags |= FOLL_NOFAULT;



		addr = first_iovec_segment(i, &len, start, maxsize, ~0U);

		n = DIV_ROUND_UP(len, PAGE_SIZE);

		p = get_pages_array(n);

		if (!p)

			return -ENOMEM;

		res = get_user_pages_fast(addr, n,

				iov_iter_rw(i) != WRITE ?  FOLL_WRITE : 0, p);

		res = get_user_pages_fast(addr, n, gup_flags, p);

		if (unlikely(res <= 0)) {

			kvfree(p);

			*pages = NULL;