Replace hugetlbfs_read_iter() with generic_file_read_iter(),
teach filemap_get_pages() to be aware of hugetlb pagesize while
calculating 'last_index'.

[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 | 84 +-------------------------------------------
 mm/filemap.c         | 15 ++++++--
 2 files changed, 14 insertions(+), 85 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index f1f8c3f7388f..1c25485c91b9 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -187,88 +187,6 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	return mm_get_unmapped_area_vmflags(file, addr0, len, pgoff, flags, 0);
 }
 
-/*
- * Support for read() - Find the page attached to f_mapping and copy out the
- * data. This provides functionality similar to filemap_read().
- */
-static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
-{
-	struct file *file = iocb->ki_filp;
-	struct hstate *h = hstate_file(file);
-	struct address_space *mapping = file->f_mapping;
-	struct inode *inode = mapping->host;
-	unsigned long index = iocb->ki_pos >> huge_page_shift(h);
-	unsigned long offset = iocb->ki_pos & ~huge_page_mask(h);
-	unsigned long end_index;
-	loff_t isize;
-	ssize_t retval = 0;
-
-	while (iov_iter_count(to)) {
-		struct folio *folio;
-		size_t nr, copied, want;
-
-		/* nr is the maximum number of bytes to copy from this page */
-		nr = huge_page_size(h);
-		isize = i_size_read(inode);
-		if (!isize)
-			break;
-		end_index = (isize - 1) >> huge_page_shift(h);
-		if (index > end_index)
-			break;
-		if (index == end_index) {
-			nr = ((isize - 1) & ~huge_page_mask(h)) + 1;
-			if (nr <= offset)
-				break;
-		}
-		nr = nr - offset;
-
-		/* Find the folio */
-		folio = filemap_lock_hugetlb_folio(h, mapping, index);
-		if (IS_ERR(folio)) {
-			/*
-			 * We have a HOLE, zero out the user-buffer for the
-			 * length of the hole or request.
-			 */
-			copied = iov_iter_zero(nr, to);
-		} else {
-			folio_unlock(folio);
-
-			if (!folio_test_hwpoison(folio))
-				want = nr;
-			else {
-				/*
-				 * Adjust how many bytes safe to read without
-				 * touching the 1st raw HWPOISON page after
-				 * offset.
-				 */
-				want = adjust_range_hwpoison(folio, offset, nr);
-				if (want == 0) {
-					folio_put(folio);
-					retval = -EIO;
-					break;
-				}
-			}
-
-			/*
-			 * We have the folio, copy it to user space buffer.
-			 */
-			copied = copy_folio_to_iter(folio, offset, want, to);
-			folio_put(folio);
-		}
-		offset += copied;
-		retval += copied;
-		if (copied != nr && iov_iter_count(to)) {
-			if (!retval)
-				retval = -EFAULT;
-			break;
-		}
-		index += offset >> huge_page_shift(h);
-		offset &= ~huge_page_mask(h);
-	}
-	iocb->ki_pos = ((loff_t)index << huge_page_shift(h)) + offset;
-	return retval;
-}
-
 static int hugetlbfs_write_begin(const struct kiocb *iocb,
 			struct address_space *mapping,
 			loff_t pos, unsigned len,
@@ -1181,7 +1099,7 @@ static void init_once(void *foo)
 }
 
 static const struct file_operations hugetlbfs_file_operations = {
-	.read_iter		= hugetlbfs_read_iter,
+	.read_iter		= generic_file_read_iter,
 	.mmap			= hugetlbfs_file_mmap,
 	.fsync			= noop_fsync,
 	.get_unmapped_area	= hugetlb_get_unmapped_area,
diff --git a/mm/filemap.c b/mm/filemap.c
index df8543573570..eb03b31791fc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2672,20 +2672,30 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 {
 	struct file *filp = iocb->ki_filp;
 	struct address_space *mapping = filp->f_mapping;
+	bool is_hugetlbfs = is_file_hugepages(filp);
 	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
 	pgoff_t last_index;
 	struct folio *folio;
 	unsigned int flags;
+	size_t min_folio_bytes;
 	int err = 0;
 
 	/* "last_index" is the index of the folio beyond the end of the read */
-	last_index = round_up(iocb->ki_pos + count,
-			mapping_min_folio_nrbytes(mapping)) >> PAGE_SHIFT;
+	if (is_hugetlbfs)
+		min_folio_bytes = huge_page_size(hstate_file(filp));
+	else
+		min_folio_bytes = mapping_min_folio_nrbytes(mapping);
+	last_index = round_up(iocb->ki_pos + count, min_folio_bytes) >> PAGE_SHIFT;
+
 retry:
 	if (fatal_signal_pending(current))
 		return -EINTR;
 
 	filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
+
+	if (is_hugetlbfs)
+		goto done;
+
 	if (!folio_batch_count(fbatch)) {
 		DEFINE_READAHEAD(ractl, filp, &filp->f_ra, mapping, index);
 
@@ -2724,6 +2734,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 			goto err;
 	}
 
+done:
 	trace_mm_filemap_get_pages(mapping, index, last_index - 1);
 	return 0;
 err:
-- 
2.43.5