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Subject[PATCH 2/6] iov_iter: new iov_iter_pin_pages*(), for FOLL_PIN pages
Date
From: John Hubbard <jhubbard@nvidia.com>

Provide two new specialized routines that only handle user space pages,
and invoke pin_user_pages_fast() on them: iov_iter_pin_pages() and
iov_iter_pin_pages_alloc().

This allows subsequent patches to convert various callers of
iov_iter_get_pages*(), to the new calls, without having to attempt a
mass conversion all at once.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/uio.h | 4 +++
lib/iov_iter.c | 78 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 739285fe5a2f..208020c2b75a 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -236,6 +236,10 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
size_t maxsize, unsigned maxpages, size_t *start);
ssize_t iov_iter_get_pages_alloc(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);

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6dd5330f7a99..e64e8e4edd0c 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1560,6 +1560,41 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
}
EXPORT_SYMBOL(iov_iter_get_pages);

+ssize_t iov_iter_pin_pages(struct iov_iter *i,
+ struct page **pages, size_t maxsize, unsigned int maxpages,
+ size_t *start)
+{
+ size_t len;
+ int n, res;
+
+ if (maxsize > i->count)
+ maxsize = i->count;
+ if (!maxsize)
+ return 0;
+
+ WARN_ON_ONCE(!iter_is_iovec(i));
+
+ 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 = pin_user_pages_fast(addr, n, gup_flags, pages);
+ if (unlikely(res <= 0))
+ return res;
+ return (res == n ? len : res * PAGE_SIZE) - *start;
+ }
+
+ return -EFAULT;
+}
+EXPORT_SYMBOL(iov_iter_pin_pages);
+
static struct page **get_pages_array(size_t n)
{
return kvmalloc_array(n, sizeof(struct page *), GFP_KERNEL);
@@ -1696,6 +1731,49 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
}
EXPORT_SYMBOL(iov_iter_get_pages_alloc);

+ssize_t iov_iter_pin_pages_alloc(struct iov_iter *i,
+ struct page ***pages, size_t maxsize,
+ size_t *start)
+{
+ struct page **p;
+ size_t len;
+ int n, res;
+
+ if (maxsize > i->count)
+ maxsize = i->count;
+ if (!maxsize)
+ return 0;
+
+ WARN_ON_ONCE(!iter_is_iovec(i));
+
+ 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 = pin_user_pages_fast(addr, n, gup_flags, p);
+ if (unlikely(res <= 0)) {
+ kvfree(p);
+ *pages = NULL;
+ return res;
+ }
+ *pages = p;
+ return (res == n ? len : res * PAGE_SIZE) - *start;
+ }
+
+ return -EFAULT;
+}
+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)
{
--
2.35.1
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