[PATCH 6.7 041/713] dm-verity, dm-crypt: align "struct bvec_iter" correctly

Sasha Levin
2024-03-24T22:48:01Z

From: Mikulas Patocka <mpatocka@redhat.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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 4ab4e8dcfd3e2..35f50193959e0 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -53,11 +53,11 @@
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 4620a98c99561..db93a91169d5e 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -80,12 +80,12 @@ 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 int n_blocks;
bool in_tasklet;

- struct bvec_iter iter;
-
struct work_struct work;

char *recheck_buffer;
--
2.43.0