[PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

From: Pankaj Raghav <p.raghav@samsung.com>

iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
< fs block size. iomap_dio_zero() has an implicit assumption that fs block
size < page_size. This is true for most filesystems at the moment.

If the block size > page size, this will send the contents of the page
next to zero page(as len > PAGE_SIZE) to the underlying block device,
causing FS corruption.

iomap is a generic infrastructure and it should not make any assumptions
about the fs block size and the page size of the system.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
---
 fs/iomap/buffered-io.c |  4 ++--
 fs/iomap/direct-io.c   | 30 ++++++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f420c53d86ac..9a9e94c7ed1d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
 }
 EXPORT_SYMBOL_GPL(iomap_writepages);
 
-static int __init iomap_init(void)
+static int __init iomap_pagecache_init(void)
 {
 	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
 			   offsetof(struct iomap_ioend, io_bio),
 			   BIOSET_NEED_BVECS);
 }
-fs_initcall(iomap_init);
+fs_initcall(iomap_pagecache_init);
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index f3b43d223a46..61d09d2364f7 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -11,6 +11,7 @@
 #include <linux/iomap.h>
 #include <linux/backing-dev.h>
 #include <linux/uio.h>
+#include <linux/set_memory.h>
 #include <linux/task_io_accounting_ops.h>
 #include "trace.h"
 
@@ -27,6 +28,13 @@
 #define IOMAP_DIO_WRITE		(1U << 30)
 #define IOMAP_DIO_DIRTY		(1U << 31)
 
+/*
+ * Used for sub block zeroing in iomap_dio_zero()
+ */
+#define ZERO_PAGE_64K_SIZE (65536)
+#define ZERO_PAGE_64K_ORDER (get_order(ZERO_PAGE_64K_SIZE))
+static struct page *zero_page_64k;
+
 struct iomap_dio {
 	struct kiocb		*iocb;
 	const struct iomap_dio_ops *dops;
@@ -236,9 +244,13 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		loff_t pos, unsigned len)
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
-	struct page *page = ZERO_PAGE(0);
 	struct bio *bio;
 
+	/*
+	 * Max block size supported is 64k
+	 */
+	WARN_ON_ONCE(len > ZERO_PAGE_64K_SIZE);
+
 	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 				  GFP_KERNEL);
@@ -246,7 +258,7 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	__bio_add_page(bio, page, len, 0);
+	__bio_add_page(bio, zero_page_64k, len, 0);
 	iomap_dio_submit_bio(iter, dio, bio, pos);
 }
 
@@ -753,3 +765,17 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return iomap_dio_complete(dio);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
+
+static int __init iomap_dio_init(void)
+{
+	zero_page_64k = alloc_pages(GFP_KERNEL | __GFP_ZERO,
+				    ZERO_PAGE_64K_ORDER);
+
+	if (!zero_page_64k)
+		return -ENOMEM;
+
+	set_memory_ro((unsigned long)page_address(zero_page_64k),
+		      1U << ZERO_PAGE_64K_ORDER);
+	return 0;
+}
+fs_initcall(iomap_dio_init);
-- 
2.44.1