[PATCH RFC v3 34/36] kmsan: disable physical page merging in biovec

[glider@google.com]

KMSAN metadata for consequent physical pages may be inconsequent,
therefore accessing such pages together may lead to metadata
corruption.
We disable merging pages in biovec to prevent such corruptions.

Signed-off-by: Alexander Potapenko <glider@google.com>
To: Alexander Potapenko <glider@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: linux-mm@kvack.org
---

Change-Id: Id2f2babaf662ac44675c4f2790f4a80ddc328fa7
---
 block/blk.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/blk.h b/block/blk.h
index 47fba9362e60..9ee271a22423 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -78,6 +78,13 @@ static inline bool biovec_phys_mergeable(struct request_queue *q,
 	phys_addr_t addr1 = page_to_phys(vec1->bv_page) + vec1->bv_offset;
 	phys_addr_t addr2 = page_to_phys(vec2->bv_page) + vec2->bv_offset;
 
+#ifdef CONFIG_KMSAN
+	/*
+	 * Merging consequent physical pages may not work correctly under KMSAN
+	 * if their metadata pages aren't consequent. Just disable merging.
+	 */
+	return false;
+#endif
 	if (addr1 + vec1->bv_len != addr2)
 		return false;
 	if (xen_domain() && !xen_biovec_phys_mergeable(vec1, vec2->bv_page))
-- 
2.24.0.432.g9d3f5f5b63-goog