[PATCH 5.15 28/33] iov_iter: Introduce nofault flag to disable page faults

Greg Kroah-Hartman
2022-04-29T10:45:56Z

From: Andreas Gruenbacher <agruenba@redhat.com>

commit 3337ab08d08b1a375f88471d9c8b1cac968cb054 upstream

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: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/uio.h | 1 +
lib/iov_iter.c | 20 +++++++++++++++-----
2 files changed, 16 insertions(+), 5 deletions(-)

--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -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;
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -514,6 +514,7 @@ void iov_iter_init(struct iov_iter *i, u
WARN_ON(direction & ~(READ | WRITE));
*i = (struct iov_iter) {
.iter_type = ITER_IOVEC,
+ .nofault = false,
.data_source = direction,
.iov = iov,
.nr_segs = nr_segs,
@@ -1529,13 +1530,17 @@ ssize_t iov_iter_get_pages(struct iov_it
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;
@@ -1651,15 +1656,20 @@ ssize_t iov_iter_get_pages_alloc(struct
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;