[PATCH 3/3] iov: Remove copy_page_from_iter_atomic()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

All callers now use copy_folio_from_iter_atomic(), so convert
copy_page_from_iter_atomic().  While I'm in there, use kmap_local_folio()
and pagefault_disable() instead of kmap_atomic().  That allows preemption
and/or task migration to happen during the copy_from_user().  Also use
the new folio_test_partial_kmap() predicate instead of open-coding it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/uio.h | 10 ++--------
 lib/iov_iter.c      | 29 +++++++++++++----------------
 2 files changed, 15 insertions(+), 24 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 49ece9e1888f..e46477482663 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -176,8 +176,6 @@ static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
 	return ret;
 }
 
-size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
-				  size_t bytes, struct iov_iter *i);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 void iov_iter_revert(struct iov_iter *i, size_t bytes);
 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes);
@@ -187,6 +185,8 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
+size_t copy_folio_from_iter_atomic(struct folio *folio, size_t offset,
+		size_t bytes, struct iov_iter *i);
 
 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
@@ -204,12 +204,6 @@ static inline size_t copy_folio_from_iter(struct folio *folio, size_t offset,
 	return copy_page_from_iter(&folio->page, offset, bytes, i);
 }
 
-static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
-		size_t offset, size_t bytes, struct iov_iter *i)
-{
-	return copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
-}
-
 size_t copy_page_to_iter_nofault(struct page *page, unsigned offset,
 				 size_t bytes, struct iov_iter *i);
 
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index d9e19fb2dcf3..969d4ad510df 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -457,38 +457,35 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 }
 EXPORT_SYMBOL(iov_iter_zero);
 
-size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
+size_t copy_folio_from_iter_atomic(struct folio *folio, size_t offset,
 		size_t bytes, struct iov_iter *i)
 {
 	size_t n, copied = 0;
-	bool uses_kmap = IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) ||
-			 PageHighMem(page);
 
-	if (!page_copy_sane(page, offset, bytes))
+	if (!page_copy_sane(&folio->page, offset, bytes))
 		return 0;
 	if (WARN_ON_ONCE(!i->data_source))
 		return 0;
 
 	do {
-		char *p;
+		char *to = kmap_local_folio(folio, offset);
 
 		n = bytes - copied;
-		if (uses_kmap) {
-			page += offset / PAGE_SIZE;
-			offset %= PAGE_SIZE;
-			n = min_t(size_t, n, PAGE_SIZE - offset);
-		}
-
-		p = kmap_atomic(page) + offset;
-		n = __copy_from_iter(p, n, i);
-		kunmap_atomic(p);
+		if (folio_test_partial_kmap(folio) &&
+		    n > PAGE_SIZE - offset_in_page(offset))
+			n = PAGE_SIZE - offset_in_page(offset);
+
+		pagefault_disable();
+		n = __copy_from_iter(to, n, i);
+		pagefault_enable();
+		kunmap_local(to);
 		copied += n;
 		offset += n;
-	} while (uses_kmap && copied != bytes && n > 0);
+	} while (copied != bytes && n > 0);
 
 	return copied;
 }
-EXPORT_SYMBOL(copy_page_from_iter_atomic);
+EXPORT_SYMBOL(copy_folio_from_iter_atomic);
 
 static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
 {
-- 
2.47.2