linux-kernel - [PATCH AUTOSEL 5.10 8/8] dm-verity, dm-crypt: align "struct bvec

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Date: Thu, 29 Feb 2024 15:41:25 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Mikulas Patocka <mpatocka@...hat.com>,
	Mike Snitzer <snitzer@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	agk@...hat.com,
	dm-devel@...ts.linux.dev
Subject: [PATCH AUTOSEL 5.10 8/8] dm-verity, dm-crypt: align "struct bvec_iter" correctly

From: Mikulas Patocka <mpatocka@...hat.com>

[ Upstream commit 787f1b2800464aa277236a66eb3c279535edd460 ]

"struct bvec_iter" is defined with the __packed attribute, so it is
aligned on a single byte. On X86 (and on other architectures that support
unaligned addresses in hardware), "struct bvec_iter" is accessed using the
8-byte and 4-byte memory instructions, however these instructions are less
efficient if they operate on unaligned addresses.

(on RISC machines that don't have unaligned access in hardware, GCC
generates byte-by-byte accesses that are very inefficient - see [1])

This commit reorders the entries in "struct dm_verity_io" and "struct
convert_context", so that "struct bvec_iter" is aligned on 8 bytes.

[1] https://lore.kernel.org/all/ZcLuWUNRZadJr0tQ@fedora/T/

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/dm-crypt.c  | 4 ++--
 drivers/md/dm-verity.h | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 5d772f322a245..bed685969ad49 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -48,11 +48,11 @@
 struct convert_context {
 	struct completion restart;
 	struct bio *bio_in;
-	struct bio *bio_out;
 	struct bvec_iter iter_in;
+	struct bio *bio_out;
 	struct bvec_iter iter_out;
-	u64 cc_sector;
 	atomic_t cc_pending;
+	u64 cc_sector;
 	union {
 		struct skcipher_request *req;
 		struct aead_request *req_aead;
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 78d1e51195ada..f61c89c79cf5b 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -74,11 +74,11 @@ struct dm_verity_io {
 	/* original value of bio->bi_end_io */
 	bio_end_io_t *orig_bi_end_io;
 
+	struct bvec_iter iter;
+
 	sector_t block;
 	unsigned n_blocks;
 
-	struct bvec_iter iter;
-
 	struct work_struct work;
 
 	/*
-- 
2.43.0