[RFC,iov_iter v2 3/8] iov_iter: add copyin_iovec helper

[Joe Damato <jdamato@fastly.com>]

copyin_iovec is a helper which wraps copyin and selects the right copy
method based on the iter_copy_type.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 lib/iov_iter.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index d32d7e5..6720cb2 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -168,6 +168,15 @@ static int copyin(void *to, const void __user *from, size_t n)
 	return n;
 }
 
+static int copyin_iovec(void *to, const void __user *from, size_t n,
+			struct iov_iter *i)
+{
+	if (unlikely(iov_iter_copy_is_nt(i)))
+		return __copy_from_user_nocache(to, from, n);
+	else
+		return copyin(to, from, n);
+}
+
 static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i)
 {
@@ -278,7 +287,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
 		to = kaddr + offset;
 
 		/* first chunk, usually the only one */
-		left = copyin(to, buf, copy);
+		left = copyin_iovec(to, buf, copy, i);
 		copy -= left;
 		skip += copy;
 		to += copy;
@@ -288,7 +297,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
 			iov++;
 			buf = iov->iov_base;
 			copy = min(bytes, iov->iov_len);
-			left = copyin(to, buf, copy);
+			left = copyin_iovec(to, buf, copy, i);
 			copy -= left;
 			skip = copy;
 			to += copy;
@@ -307,7 +316,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
 
 	kaddr = kmap(page);
 	to = kaddr + offset;
-	left = copyin(to, buf, copy);
+	left = copyin_iovec(to, buf, copy, i);
 	copy -= left;
 	skip += copy;
 	to += copy;
@@ -316,7 +325,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
 		iov++;
 		buf = iov->iov_base;
 		copy = min(bytes, iov->iov_len);
-		left = copyin(to, buf, copy);
+		left = copyin_iovec(to, buf, copy, i);
 		copy -= left;
 		skip = copy;
 		to += copy;
@@ -766,7 +775,7 @@ size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 	if (iter_is_iovec(i))
 		might_fault();
 	iterate_and_advance(i, bytes, base, len, off,
-		copyin(addr + off, base, len),
+		copyin_iovec(addr + off, base, len, i),
 		memcpy(addr + off, base, len)
 	)
 
-- 
2.7.4