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iov_iter: Introduce nofault flag to disable page faults

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commit 3337ab08d0 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>
This commit is contained in:
Andreas Gruenbacher 2022-04-15 06:28:52 +08:00 committed by Greg Kroah-Hartman
parent 6e213bc614
commit f86f8d2784
2 changed files with 16 additions and 5 deletions
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1
include/linux/uio.h
View file

@ -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;

20
lib/iov_iter.c
View file

@ -514,6 +514,7 @@ 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,
@ -1529,13 +1530,17 @@ 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;
@ -1651,15 +1656,20 @@ 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;