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dm verity: Add optional "try_verify_in_tasklet" feature

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Using tasklets for disk verification can reduce IO latency. When there
are accelerated hash instructions it is often better to compute the
hash immediately using a tasklet rather than deferring verification to
a work-queue. This reduces time spent waiting to schedule work-queue
jobs, but requires spending slightly more time in interrupt context.

If the dm-bufio cache does not have the required hashes we fallback to
the work-queue implementation. FEC is only possible using work-queue
because code to support the FEC feature may sleep.

The following shows a speed comparison of random reads on a dm-verity
device. The dm-verity device uses a 1G ramdisk for data and a 1G
ramdisk for hashes. One test was run using tasklets and one test was
run using the existing work-queue solution. Both tests were run when
the dm-bufio cache was hot. The tasklet implementation performs
significantly better since there is no time spent waiting for
work-queue jobs to be scheduled.

   READ: bw=181MiB/s (190MB/s), 181MiB/s-181MiB/s (190MB/s-190MB/s),
   io=512MiB (537MB), run=2827-2827msec
   READ: bw=23.6MiB/s (24.8MB/s), 23.6MiB/s-23.6MiB/s (24.8MB/s-24.8MB/s),
   io=512MiB (537MB), run=21688-21688msec

Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Nathan Huckleberry 2022-07-22 09:38:23 +00:00 committed by Mike Snitzer
parent b32d45824a
commit 5721d4e5a9
2 changed files with 91 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
drivers/md/dm-verity-target.c
View File

@ -34,6 +34,7 @@
#define DM_VERITY_OPT_PANIC "panic_on_corruption"
#define DM_VERITY_OPT_IGN_ZEROES "ignore_zero_blocks"
#define DM_VERITY_OPT_AT_MOST_ONCE "check_at_most_once"
#define DM_VERITY_OPT_TASKLET_VERIFY "try_verify_in_tasklet"
#define DM_VERITY_OPTS_MAX (3 + DM_VERITY_OPTS_FEC + \
DM_VERITY_ROOT_HASH_VERIFICATION_OPTS)
@ -220,7 +221,7 @@ static int verity_handle_err(struct dm_verity *v, enum verity_block_type type,
struct mapped_device *md = dm_table_get_md(v->ti->table);
/* Corruption should be visible in device status in all modes */
v->hash_failed = 1;
v->hash_failed = true;
if (v->corrupted_errs >= DM_VERITY_MAX_CORRUPTED_ERRS)
goto out;
@ -286,7 +287,19 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
verity_hash_at_level(v, block, level, &hash_block, &offset);
data = dm_bufio_read(v->bufio, hash_block, &buf);
if (io->in_tasklet) {
data = dm_bufio_get(v->bufio, hash_block, &buf);
if (data == NULL) {
/*
* In tasklet and the hash was not in the bufio cache.
* Return early and resume execution from a work-queue
* to read the hash from disk.
*/
return -EAGAIN;
}
} else
data = dm_bufio_read(v->bufio, hash_block, &buf);
if (IS_ERR(data))
return PTR_ERR(data);
@ -307,6 +320,14 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
if (likely(memcmp(verity_io_real_digest(v, io), want_digest,
v->digest_size) == 0))
aux->hash_verified = 1;
else if (io->in_tasklet) {
/*
* Error handling code (FEC included) cannot be run in a
* tasklet since it may sleep, so fallback to work-queue.
*/
r = -EAGAIN;
goto release_ret_r;
}
else if (verity_fec_decode(v, io,
DM_VERITY_BLOCK_TYPE_METADATA,
hash_block, data, NULL) == 0)
@ -474,9 +495,14 @@ static int verity_verify_io(struct dm_verity_io *io)
bool is_zero;
struct dm_verity *v = io->v;
struct bvec_iter start;
unsigned b;
/*
* Copy the iterator in case we need to restart verification in a
* work-queue.
*/
struct bvec_iter iter_copy = io->iter;
struct crypto_wait wait;
struct bio *bio = dm_bio_from_per_bio_data(io, v->ti->per_io_data_size);
unsigned int b;
for (b = 0; b < io->n_blocks; b++) {
int r;
@ -485,7 +511,7 @@ static int verity_verify_io(struct dm_verity_io *io)
if (v->validated_blocks &&
likely(test_bit(cur_block, v->validated_blocks))) {
verity_bv_skip_block(v, io, &io->iter);
verity_bv_skip_block(v, io, &iter_copy);
continue;
}
@ -500,7 +526,7 @@ static int verity_verify_io(struct dm_verity_io *io)
* If we expect a zero block, don't validate, just
* return zeros.
*/
r = verity_for_bv_block(v, io, &io->iter,
r = verity_for_bv_block(v, io, &iter_copy,
verity_bv_zero);
if (unlikely(r < 0))
return r;
@ -512,8 +538,8 @@ static int verity_verify_io(struct dm_verity_io *io)
if (unlikely(r < 0))
return r;
start = io->iter;
r = verity_for_io_block(v, io, &io->iter, &wait);
start = iter_copy;
r = verity_for_io_block(v, io, &iter_copy, &wait);
if (unlikely(r < 0))
return r;
@ -527,8 +553,14 @@ static int verity_verify_io(struct dm_verity_io *io)
if (v->validated_blocks)
set_bit(cur_block, v->validated_blocks);
continue;
} else if (io->in_tasklet) {
/*
* Error handling code (FEC included) cannot be run in a
* tasklet since it may sleep, so fallback to work-queue.
*/
return -EAGAIN;
} else if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_DATA,
cur_block, NULL, &start) == 0) {
cur_block, NULL, &start) == 0) {
continue;
} else {
if (bio->bi_status) {
@ -566,7 +598,8 @@ static void verity_finish_io(struct dm_verity_io *io, blk_status_t status)
bio->bi_end_io = io->orig_bi_end_io;
bio->bi_status = status;
verity_fec_finish_io(io);
if (!io->in_tasklet)
verity_fec_finish_io(io);
bio_endio(bio);
}
@ -575,9 +608,29 @@ static void verity_work(struct work_struct *w)
{
struct dm_verity_io *io = container_of(w, struct dm_verity_io, work);
io->in_tasklet = false;
verity_fec_init_io(io);
verity_finish_io(io, errno_to_blk_status(verity_verify_io(io)));
}
static void verity_tasklet(unsigned long data)
{
struct dm_verity_io *io = (struct dm_verity_io *)data;
int err;
io->in_tasklet = true;
err = verity_verify_io(io);
if (err == -EAGAIN) {
/* fallback to retrying with work-queue */
INIT_WORK(&io->work, verity_work);
queue_work(io->v->verify_wq, &io->work);
return;
}
verity_finish_io(io, errno_to_blk_status(err));
}
static void verity_end_io(struct bio *bio)
{
struct dm_verity_io *io = bio->bi_private;
@ -588,8 +641,13 @@ static void verity_end_io(struct bio *bio)
return;
}
INIT_WORK(&io->work, verity_work);
queue_work(io->v->verify_wq, &io->work);
if (io->v->use_tasklet) {
tasklet_init(&io->tasklet, verity_tasklet, (unsigned long)io);
tasklet_schedule(&io->tasklet);
} else {
INIT_WORK(&io->work, verity_work);
queue_work(io->v->verify_wq, &io->work);
}
}
/*
@ -700,8 +758,6 @@ static int verity_map(struct dm_target *ti, struct bio *bio)
bio->bi_private = io;
io->iter = bio->bi_iter;
verity_fec_init_io(io);
verity_submit_prefetch(v, io);
submit_bio_noacct(bio);
@ -751,6 +807,8 @@ static void verity_status(struct dm_target *ti, status_type_t type,
args++;
if (v->validated_blocks)
args++;
if (v->use_tasklet)
args++;
if (v->signature_key_desc)
args += DM_VERITY_ROOT_HASH_VERIFICATION_OPTS;
if (!args)
@ -776,6 +834,8 @@ static void verity_status(struct dm_target *ti, status_type_t type,
DMEMIT(" " DM_VERITY_OPT_IGN_ZEROES);
if (v->validated_blocks)
DMEMIT(" " DM_VERITY_OPT_AT_MOST_ONCE);
if (v->use_tasklet)
DMEMIT(" " DM_VERITY_OPT_TASKLET_VERIFY);
sz = verity_fec_status_table(v, sz, result, maxlen);
if (v->signature_key_desc)
DMEMIT(" " DM_VERITY_ROOT_HASH_VERIFICATION_OPT_SIG_KEY
@ -1011,11 +1071,16 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
return r;
continue;
} else if (!strcasecmp(arg_name, DM_VERITY_OPT_TASKLET_VERIFY)) {
v->use_tasklet = true;
continue;
} else if (verity_is_fec_opt_arg(arg_name)) {
r = verity_fec_parse_opt_args(as, v, &argc, arg_name);
if (r)
return r;
continue;
} else if (verity_verify_is_sig_opt_arg(arg_name)) {
r = verity_verify_sig_parse_opt_args(as, v,
verify_args,
@ -1023,7 +1088,6 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
if (r)
return r;
continue;
}
ti->error = "Unrecognized verity feature request";
@ -1155,7 +1219,11 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
goto bad;
}
v->tfm = crypto_alloc_ahash(v->alg_name, 0, 0);
/*
* FIXME: CRYPTO_ALG_ASYNC should be conditional on v->use_tasklet
* but verity_parse_opt_args() happens below and has data dep on tfm.
*/
v->tfm = crypto_alloc_ahash(v->alg_name, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(v->tfm)) {
ti->error = "Cannot initialize hash function";
r = PTR_ERR(v->tfm);
@ -1265,7 +1333,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
v->bufio = dm_bufio_client_create(v->hash_dev->bdev,
1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux),
dm_bufio_alloc_callback, NULL, 0);
dm_bufio_alloc_callback, NULL,
v->use_tasklet ? DM_BUFIO_CLIENT_NO_SLEEP : 0);
if (IS_ERR(v->bufio)) {
ti->error = "Cannot initialize dm-bufio";
r = PTR_ERR(v->bufio);
@ -1312,7 +1381,7 @@ bad:
static struct target_type verity_target = {
.name = "verity",
.features = DM_TARGET_IMMUTABLE,
.version = {1, 8, 0},
.version = {1, 9, 0},
.module = THIS_MODULE,
.ctr = verity_ctr,
.dtr = verity_dtr,

6
drivers/md/dm-verity.h
View File

@ -13,6 +13,7 @@
#include <linux/dm-bufio.h>
#include <linux/device-mapper.h>
#include <linux/interrupt.h>
#include <crypto/hash.h>
#define DM_VERITY_MAX_LEVELS 63
@ -51,9 +52,10 @@ struct dm_verity {
unsigned char hash_per_block_bits; /* log2(hashes in hash block) */
unsigned char levels; /* the number of tree levels */
unsigned char version;
bool hash_failed:1; /* set if hash of any block failed */
bool use_tasklet:1; /* try to verify in tasklet before work-queue */
unsigned digest_size; /* digest size for the current hash algorithm */
unsigned int ahash_reqsize;/* the size of temporary space for crypto */
int hash_failed; /* set to 1 if hash of any block failed */
enum verity_mode mode; /* mode for handling verification errors */
unsigned corrupted_errs;/* Number of errors for corrupted blocks */
@ -76,10 +78,12 @@ struct dm_verity_io {
sector_t block;
unsigned n_blocks;
bool in_tasklet;
struct bvec_iter iter;
struct work_struct work;
struct tasklet_struct tasklet;
/*
* Three variably-size fields follow this struct: