The patch titled
Subject: iov_iter: new iov_iter_pin_pages*() routines
has been added to the -mm mm-unstable branch. Its filename is
iov_iter-new-iov_iter_pin_pages-routines.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/iov_iter-new-iov_iter_pin_pages-routines.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: iov_iter: new iov_iter_pin_pages*() routines
Date: Tue, 30 Aug 2022 21:18:40 -0700
Provide two new wrapper routines that are intended for user space pages
only:
iov_iter_pin_pages()
iov_iter_pin_pages_alloc()
Internally, these routines call pin_user_pages_fast(), instead of
get_user_pages_fast(), for user_backed_iter(i) and iov_iter_bvec(i)
cases.
As always, callers must use unpin_user_pages() or a suitable FOLL_PIN
variant, to release the pages, if they actually were acquired via
pin_user_pages_fast().
This is a prerequisite to converting bio/block layers over to use
pin_user_pages_fast().
Link: https://lkml.kernel.org/r/20220831041843.973026-5-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Anna Schumaker <anna@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/uio.h | 4 +
lib/iov_iter.c | 86 +++++++++++++++++++++++++++++++++++++++---
2 files changed, 84 insertions(+), 6 deletions(-)
--- a/include/linux/uio.h~iov_iter-new-iov_iter_pin_pages-routines
+++ a/include/linux/uio.h
@@ -251,6 +251,10 @@ ssize_t iov_iter_get_pages2(struct iov_i
size_t maxsize, unsigned maxpages, size_t *start);
ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
size_t maxsize, size_t *start);
+ssize_t iov_iter_pin_pages(struct iov_iter *i, struct page **pages,
+ size_t maxsize, unsigned int maxpages, size_t *start);
+ssize_t iov_iter_pin_pages_alloc(struct iov_iter *i, struct page ***pages,
+ size_t maxsize, size_t *start);
int iov_iter_npages(const struct iov_iter *i, int maxpages);
void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state);
--- a/lib/iov_iter.c~iov_iter-new-iov_iter_pin_pages-routines
+++ a/lib/iov_iter.c
@@ -1425,9 +1425,31 @@ static struct page *first_bvec_segment(c
return page;
}
+enum pages_alloc_internal_flags {
+ USE_FOLL_GET,
+ MAYBE_USE_FOLL_PIN
+};
+
+/*
+ * Pins pages, either via get_page(), or via pin_user_page*(). The caller is
+ * responsible for tracking which pinning mechanism was used here, and releasing
+ * pages via the appropriate call: put_page() or unpin_user_page().
+ *
+ * The way to figure that out is:
+ *
+ * a) If how_to_pin == FOLL_GET, then this routine will always pin via
+ * get_page().
+ *
+ * b) If how_to_pin == MAYBE_USE_FOLL_PIN, then this routine will pin via
+ * pin_user_page*() for either user_backed_iter(i) cases, or
+ * iov_iter_is_bvec(i) cases. However, for the other cases (pipe,
+ * xarray), pages will be pinned via get_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 maxpages, size_t *start,
+ enum pages_alloc_internal_flags how_to_pin)
+
{
unsigned int n;
@@ -1454,7 +1476,12 @@ static ssize_t __iov_iter_get_pages_allo
n = want_pages_array(pages, maxsize, *start, maxpages);
if (!n)
return -ENOMEM;
- res = get_user_pages_fast(addr, n, gup_flags, *pages);
+
+ if (how_to_pin == MAYBE_USE_FOLL_PIN)
+ res = pin_user_pages_fast(addr, n, gup_flags, *pages);
+ else
+ 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);
@@ -1470,8 +1497,13 @@ static ssize_t __iov_iter_get_pages_allo
if (!n)
return -ENOMEM;
p = *pages;
- for (int k = 0; k < n; k++)
- get_page(p[k] = page + k);
+ for (int k = 0; k < n; k++) {
+ p[k] = page + k;
+ if (how_to_pin == MAYBE_USE_FOLL_PIN)
+ pin_user_page(p[k]);
+ else
+ get_page(p[k]);
+ }
maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
i->count -= maxsize;
i->iov_offset += maxsize;
@@ -1497,10 +1529,29 @@ ssize_t iov_iter_get_pages2(struct iov_i
return 0;
BUG_ON(!pages);
- return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start);
+ return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start,
+ USE_FOLL_GET);
}
EXPORT_SYMBOL(iov_iter_get_pages2);
+/*
+ * A FOLL_PIN variant that calls pin_user_pages_fast() instead of
+ * get_user_pages_fast().
+ */
+ssize_t iov_iter_pin_pages(struct iov_iter *i,
+ struct page **pages, size_t maxsize, unsigned int maxpages,
+ size_t *start)
+{
+ if (!maxpages)
+ return 0;
+ if (WARN_ON_ONCE(!pages))
+ return -EINVAL;
+
+ return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start,
+ MAYBE_USE_FOLL_PIN);
+}
+EXPORT_SYMBOL(iov_iter_pin_pages);
+
ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
struct page ***pages, size_t maxsize,
size_t *start)
@@ -1509,7 +1560,8 @@ ssize_t iov_iter_get_pages_alloc2(struct
*pages = NULL;
- len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start);
+ len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start,
+ USE_FOLL_GET);
if (len <= 0) {
kvfree(*pages);
*pages = NULL;
@@ -1518,6 +1570,28 @@ ssize_t iov_iter_get_pages_alloc2(struct
}
EXPORT_SYMBOL(iov_iter_get_pages_alloc2);
+/*
+ * A FOLL_PIN variant that calls pin_user_pages_fast() instead of
+ * get_user_pages_fast().
+ */
+ssize_t iov_iter_pin_pages_alloc(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,
+ MAYBE_USE_FOLL_PIN);
+ if (len <= 0) {
+ kvfree(*pages);
+ *pages = NULL;
+ }
+ return len;
+}
+EXPORT_SYMBOL(iov_iter_pin_pages_alloc);
+
size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
struct iov_iter *i)
{
_
Patches currently in -mm which might be from jhubbard@xxxxxxxxxx are
mm-change-release_pages-to-use-unsigned-long-for-npages.patch
mm-gup-introduce-pin_user_page.patch
block-add-dio_w_-wrappers-for-pin-unpin-user-pages.patch
iov_iter-new-iov_iter_pin_pages-routines.patch
block-bio-fs-convert-most-filesystems-to-pin_user_pages_fast.patch
nfs-direct-io-convert-to-foll_pin-pages.patch
fuse-convert-direct-io-paths-to-use-foll_pin.patch
