[PATCH v2 2/3] iov_iter: introduce iov_iter_pin_user_pages*() routines

John Hubbard
2020-08-29T08:09:19Z

The new routines are:
iov_iter_pin_user_pages()
iov_iter_pin_user_pages_alloc()

and those correspond to these pre-existing routines:
iov_iter_get_pages()
iov_iter_get_pages_alloc()

Also, pipe_get_pages() and related are changed so as to pass
down a "use_pup" (use pin_user_page() instead of get_page()) bool
argument.

Unlike the iov_iter_get_pages*() routines, the
iov_iter_pin_user_pages*() routines assert that only ITER_IOVEC or
ITER_PIPE items are passed in. They then call pin_user_page*(), instead
of get_user_pages_fast() or get_page().

Why: In order to incrementally change Direct IO callers from calling
get_user_pages_fast() and put_page(), over to calling
pin_user_pages_fast() and unpin_user_page(), there need to be mid-level
routines that specifically call one or the other systems, for both page
acquisition and page release.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/uio.h | 5 ++
lib/iov_iter.c | 110 ++++++++++++++++++++++++++++++++++++++++----
2 files changed, 107 insertions(+), 8 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 3835a8a8e9ea..29b0504a27cc 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -229,6 +229,11 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages);

const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags);

+ssize_t iov_iter_pin_user_pages(struct iov_iter *i, struct page **pages,
+ size_t maxsize, unsigned int maxpages, size_t *start);
+ssize_t iov_iter_pin_user_pages_alloc(struct iov_iter *i, struct page ***pages,
+ size_t maxsize, size_t *start);
+
static inline size_t iov_iter_count(const struct iov_iter *i)
{
return i->count;
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5e40786c8f12..f25555eb3279 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1269,7 +1269,8 @@ static inline ssize_t __pipe_get_pages(struct iov_iter *i,
size_t maxsize,
struct page **pages,
int iter_head,
- size_t *start)
+ size_t *start,
+ bool use_pup)
{
struct pipe_inode_info *pipe = i->pipe;
unsigned int p_mask = pipe->ring_size - 1;
@@ -1280,7 +1281,11 @@ static inline ssize_t __pipe_get_pages(struct iov_iter *i,
maxsize = n;
n += *start;
while (n > 0) {
- get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+ if (use_pup)
+ pin_user_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+ else
+ get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+
iter_head++;
n -= PAGE_SIZE;
}
@@ -1290,7 +1295,7 @@ static inline ssize_t __pipe_get_pages(struct iov_iter *i,

static ssize_t pipe_get_pages(struct iov_iter *i,
struct page **pages, size_t maxsize, unsigned maxpages,
- size_t *start)
+ size_t *start, bool use_pup)
{
unsigned int iter_head, npages;
size_t capacity;
@@ -1306,8 +1311,51 @@ static ssize_t pipe_get_pages(struct iov_iter *i,
npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
capacity = min(npages, maxpages) * PAGE_SIZE - *start;

- return __pipe_get_pages(i, min(maxsize, capacity), pages, iter_head, start);
+ return __pipe_get_pages(i, min(maxsize, capacity), pages, iter_head,
+ start, use_pup);
+}
+
+ssize_t iov_iter_pin_user_pages(struct iov_iter *i,
+ struct page **pages, size_t maxsize, unsigned int maxpages,
+ size_t *start)
+{
+ size_t skip = i->iov_offset;
+ const struct iovec *iov;
+ struct iovec v;
+
+ if (unlikely(iov_iter_is_pipe(i)))
+ return pipe_get_pages(i, pages, maxsize, maxpages, start, true);
+ if (unlikely(iov_iter_is_discard(i)))
+ return -EFAULT;
+ if (WARN_ON_ONCE(!iter_is_iovec(i)))
+ return -EFAULT;
+
+ if (unlikely(!maxsize))
+ return 0;
+ maxsize = min(maxsize, i->count);
+
+ iterate_iovec(i, maxsize, v, iov, skip, ({
+ unsigned long addr = (unsigned long)v.iov_base;
+ size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
+ int n;
+ int res;
+
+ if (len > maxpages * PAGE_SIZE)
+ len = maxpages * PAGE_SIZE;
+ addr &= ~(PAGE_SIZE - 1);
+ n = DIV_ROUND_UP(len, PAGE_SIZE);
+
+ res = pin_user_pages_fast(addr, n,
+ iov_iter_rw(i) != WRITE ? FOLL_WRITE : 0,
+ pages);
+ if (unlikely(res < 0))
+ return res;
+ return (res == n ? len : res * PAGE_SIZE) - *start;
+ 0;
+ }))
+ return 0;
}
+EXPORT_SYMBOL(iov_iter_pin_user_pages);

ssize_t iov_iter_get_pages(struct iov_iter *i,
struct page **pages, size_t maxsize, unsigned maxpages,
@@ -1317,7 +1365,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
maxsize = i->count;

if (unlikely(iov_iter_is_pipe(i)))
- return pipe_get_pages(i, pages, maxsize, maxpages, start);
+ return pipe_get_pages(i, pages, maxsize, maxpages, start, false);
if (unlikely(iov_iter_is_discard(i)))
return -EFAULT;

@@ -1357,7 +1405,7 @@ static struct page **get_pages_array(size_t n)

static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
struct page ***pages, size_t maxsize,
- size_t *start)
+ size_t *start, bool use_pup)
{
struct page **p;
unsigned int iter_head, npages;
@@ -1380,7 +1428,7 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
p = get_pages_array(npages);
if (!p)
return -ENOMEM;
- n = __pipe_get_pages(i, maxsize, p, iter_head, start);
+ n = __pipe_get_pages(i, maxsize, p, iter_head, start, use_pup);
if (n > 0)
*pages = p;
else
@@ -1388,6 +1436,52 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
return n;
}

+ssize_t iov_iter_pin_user_pages_alloc(struct iov_iter *i,
+ struct page ***pages, size_t maxsize,
+ size_t *start)
+{
+ struct page **p;
+ size_t skip = i->iov_offset;
+ const struct iovec *iov;
+ struct iovec v;
+
+ if (unlikely(iov_iter_is_pipe(i)))
+ return pipe_get_pages_alloc(i, pages, maxsize, start, true);
+ if (unlikely(iov_iter_is_discard(i)))
+ return -EFAULT;
+ if (WARN_ON_ONCE(!iter_is_iovec(i)))
+ return -EFAULT;
+
+ if (unlikely(!maxsize))
+ return 0;
+ maxsize = min(maxsize, i->count);
+
+ iterate_iovec(i, maxsize, v, iov, skip, ({
+ unsigned long addr = (unsigned long)v.iov_base;
+ size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
+ int n;
+ int res;
+
+ addr &= ~(PAGE_SIZE - 1);
+ n = DIV_ROUND_UP(len, PAGE_SIZE);
+ p = get_pages_array(n);
+ if (!p)
+ return -ENOMEM;
+
+ res = pin_user_pages_fast(addr, n,
+ iov_iter_rw(i) != WRITE ? FOLL_WRITE : 0, p);
+ if (unlikely(res < 0)) {
+ kvfree(p);
+ return res;
+ }
+ *pages = p;
+ return (res == n ? len : res * PAGE_SIZE) - *start;
+ 0;
+ }))
+ return 0;
+}
+EXPORT_SYMBOL(iov_iter_pin_user_pages_alloc);
+
ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
struct page ***pages, size_t maxsize,
size_t *start)
@@ -1398,7 +1492,7 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
maxsize = i->count;

if (unlikely(iov_iter_is_pipe(i)))
- return pipe_get_pages_alloc(i, pages, maxsize, start);
+ return pipe_get_pages_alloc(i, pages, maxsize, start, false);
if (unlikely(iov_iter_is_discard(i)))
return -EFAULT;

--
2.28.0