The functionality and implementation of adjust_range_hwpoison() is
generic, so factor it out and make it ready for generic use.

[1] https://lore.kernel.org/linux-mm/aeZwAz6PcdlqSnJ2@casper.infradead.org/

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
---
 fs/hugetlbfs/inode.c    | 25 -------------------------
 include/linux/fs.h      |  2 ++
 include/linux/hugetlb.h |  5 -----
 mm/filemap.c            | 31 +++++++++++++++++++++++++++++++
 4 files changed, 33 insertions(+), 30 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 66520f7c53c6..f1f8c3f7388f 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -187,31 +187,6 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	return mm_get_unmapped_area_vmflags(file, addr0, len, pgoff, flags, 0);
 }
 
-/*
- * Someone wants to read @bytes from a HWPOISON hugetlb @folio from @offset.
- * Returns the maximum number of bytes one can read without touching the 1st raw
- * HWPOISON page.
- */
-static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
-		size_t bytes)
-{
-	struct page *page = folio_page(folio, offset / PAGE_SIZE);
-	size_t safe_bytes;
-
-	if (is_raw_hwpoison_page_in_folio(page))
-		return 0;
-	/* Safe to read the remaining bytes in this page. */
-	safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
-	page++;
-
-	/* Check each remaining page as long as we are not done yet. */
-	for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
-		if (is_raw_hwpoison_page_in_folio(page))
-			break;
-
-	return min(safe_bytes, bytes);
-}
-
 /*
  * Support for read() - Find the page attached to f_mapping and copy out the
  * data. This provides functionality similar to filemap_read().
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 11559c513dfb..3876d5beda58 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3052,6 +3052,8 @@ int generic_write_checks_count(struct kiocb *iocb, loff_t *count);
 extern int generic_write_check_limits(struct file *file, loff_t pos,
 		loff_t *count);
 extern int generic_file_rw_checks(struct file *file_in, struct file *file_out);
+bool is_raw_hwpoison_page_in_folio(struct page *page);
+size_t adjust_range_hwpoison(struct folio *folio, size_t offset, size_t bytes);
 ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *to,
 		ssize_t already_read);
 extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index a9846f043712..218284e80451 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1078,11 +1078,6 @@ void hugetlb_register_node(struct node *node);
 void hugetlb_unregister_node(struct node *node);
 #endif
 
-/*
- * Check if a given raw @page is HWPOISON in a folio of any kind
- */
-bool is_raw_hwpoison_page_in_folio(struct page *page);
-
 static inline unsigned long huge_page_mask_align(struct file *file)
 {
 	return PAGE_MASK & ~huge_page_mask(hstate_file(file));
diff --git a/mm/filemap.c b/mm/filemap.c
index 4e636647100c..a27ce4ad6247 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2753,6 +2753,37 @@ static void filemap_end_dropbehind_read(struct folio *folio)
 	}
 }
 
+/**
+ * adjust_range_hwpoison - adjust clean readable range to avoid hwpoison.
+ * @folio: folio that contains hwpoison(s).
+ * @offset: bytes into the folio where subsequent read starts.
+ * @bytes: number of bytes wish to read.
+ *
+ * Return: adjusted total number of bytes starting off @offset that can be
+ * safely read from the @folio.
+ */
+size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
+		size_t bytes)
+{
+	struct page *page = folio_page(folio, offset / PAGE_SIZE);
+	size_t safe_bytes;
+
+	if (is_raw_hwpoison_page_in_folio(page))
+		return 0;
+
+	/* Safe to read the remaining bytes in this page. */
+	safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
+	page++;
+
+	/* Check each remaining page as long as we are not done yet. */
+	for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
+		if (is_raw_hwpoison_page_in_folio(page))
+			break;
+
+	return min(safe_bytes, bytes);
+}
+EXPORT_SYMBOL_GPL(adjust_range_hwpoison);
+
 /**
  * filemap_read - Read data from the page cache.
  * @iocb: The iocb to read.
-- 
2.43.5