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blk-crypto: optimize bio splitting in blk_crypto_fallback_encrypt_bio

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The current code in blk_crypto_fallback_encrypt_bio is inefficient and
prone to deadlocks under memory pressure: It first walks the passed in
plaintext bio to see how much of it can fit into a single encrypted
bio using up to BIO_MAX_VEC PAGE_SIZE segments, and then allocates a
plaintext clone that fits the size, only to allocate another bio for
the ciphertext later.  While the plaintext clone uses a bioset to avoid
deadlocks when allocations could fail, the ciphertex one uses bio_kmalloc
which is a no-go in the file system I/O path.

Switch blk_crypto_fallback_encrypt_bio to walk the source plaintext bio
while consuming bi_iter without cloning it, and instead allocate a
ciphertext bio at the beginning and whenever we fille up the previous
one.  The existing bio_set for the plaintext clones is reused for the
ciphertext bios to remove the deadlock risk.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig
2026-01-09 07:07:45 +01:00
committed by Jens Axboe
parent aefc2a1fa2
commit b37fbce460
1 changed files with 76 additions and 105 deletions
Download Patch File Download Diff File Expand all files Collapse all files

181
block/blk-crypto-fallback.c
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@@ -81,7 +81,7 @@ static struct blk_crypto_fallback_keyslot {
static struct blk_crypto_profile *blk_crypto_fallback_profile;
static struct workqueue_struct *blk_crypto_wq;
static mempool_t *blk_crypto_bounce_page_pool;
static struct bio_set crypto_bio_split;
static struct bio_set enc_bio_set;
/*
* This is the key we set when evicting a keyslot. This *should* be the all 0's
@@ -150,37 +150,29 @@ static void blk_crypto_fallback_encrypt_endio(struct bio *enc_bio)
mempool_free(enc_bio->bi_io_vec[i].bv_page,
blk_crypto_bounce_page_pool);
src_bio->bi_status = enc_bio->bi_status;
if (enc_bio->bi_status)
cmpxchg(&src_bio->bi_status, 0, enc_bio->bi_status);
bio_uninit(enc_bio);
kfree(enc_bio);
bio_put(enc_bio);
bio_endio(src_bio);
}
static struct bio *blk_crypto_fallback_clone_bio(struct bio *bio_src)
static struct bio *blk_crypto_alloc_enc_bio(struct bio *bio_src,
unsigned int nr_segs)
{
unsigned int nr_segs = bio_segments(bio_src);
struct bvec_iter iter;
struct bio_vec bv;
struct bio *bio;
bio = bio_kmalloc(nr_segs, GFP_NOIO);
if (!bio)
return NULL;
bio_init_inline(bio, bio_src->bi_bdev, nr_segs, bio_src->bi_opf);
bio = bio_alloc_bioset(bio_src->bi_bdev, nr_segs, bio_src->bi_opf,
GFP_NOIO, &enc_bio_set);
if (bio_flagged(bio_src, BIO_REMAPPED))
bio_set_flag(bio, BIO_REMAPPED);
bio->bi_private = bio_src;
bio->bi_end_io = blk_crypto_fallback_encrypt_endio;
bio->bi_ioprio = bio_src->bi_ioprio;
bio->bi_write_hint = bio_src->bi_write_hint;
bio->bi_write_stream = bio_src->bi_write_stream;
bio->bi_iter.bi_sector = bio_src->bi_iter.bi_sector;
bio->bi_iter.bi_size = bio_src->bi_iter.bi_size;
bio_for_each_segment(bv, bio_src, iter)
bio->bi_io_vec[bio->bi_vcnt++] = bv;
bio_clone_blkg_association(bio, bio_src);
return bio;
}
@@ -208,32 +200,6 @@ blk_crypto_fallback_alloc_cipher_req(struct blk_crypto_keyslot *slot,
return true;
}
static bool blk_crypto_fallback_split_bio_if_needed(struct bio **bio_ptr)
{
struct bio *bio = *bio_ptr;
unsigned int i = 0;
unsigned int num_sectors = 0;
struct bio_vec bv;
struct bvec_iter iter;
bio_for_each_segment(bv, bio, iter) {
num_sectors += bv.bv_len >> SECTOR_SHIFT;
if (++i == BIO_MAX_VECS)
break;
}
if (num_sectors < bio_sectors(bio)) {
bio = bio_submit_split_bioset(bio, num_sectors,
&crypto_bio_split);
if (!bio)
return false;
*bio_ptr = bio;
}
return true;
}
union blk_crypto_iv {
__le64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
u8 bytes[BLK_CRYPTO_MAX_IV_SIZE];
@@ -257,46 +223,35 @@ static void blk_crypto_dun_to_iv(const u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
*/
static void blk_crypto_fallback_encrypt_bio(struct bio *src_bio)
{
struct bio *enc_bio;
struct bio_crypt_ctx *bc;
struct blk_crypto_keyslot *slot;
int data_unit_size;
struct bio_crypt_ctx *bc = src_bio->bi_crypt_context;
int data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;
struct skcipher_request *ciph_req = NULL;
struct blk_crypto_keyslot *slot;
DECLARE_CRYPTO_WAIT(wait);
u64 curr_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
struct scatterlist src, dst;
union blk_crypto_iv iv;
unsigned int i, j;
blk_status_t blk_st;
/* Split the bio if it's too big for single page bvec */
if (!blk_crypto_fallback_split_bio_if_needed(&src_bio))
goto out_endio;
bc = src_bio->bi_crypt_context;
data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;
/* Allocate bounce bio for encryption */
enc_bio = blk_crypto_fallback_clone_bio(src_bio);
if (!enc_bio) {
src_bio->bi_status = BLK_STS_RESOURCE;
goto out_endio;
}
unsigned int nr_enc_pages, enc_idx;
struct bio *enc_bio;
blk_status_t status;
unsigned int i;
/*
* Get a blk-crypto-fallback keyslot that contains a crypto_skcipher for
* this bio's algorithm and key.
*/
blk_st = blk_crypto_get_keyslot(blk_crypto_fallback_profile,
status = blk_crypto_get_keyslot(blk_crypto_fallback_profile,
bc->bc_key, &slot);
if (blk_st != BLK_STS_OK) {
src_bio->bi_status = blk_st;
goto out_put_enc_bio;
if (status != BLK_STS_OK) {
src_bio->bi_status = status;
bio_endio(src_bio);
return;
}
/* and then allocate an skcipher_request for it */
if (!blk_crypto_fallback_alloc_cipher_req(slot, &ciph_req, &wait)) {
src_bio->bi_status = BLK_STS_RESOURCE;
bio_endio(src_bio);
goto out_release_keyslot;
}
@@ -307,59 +262,75 @@ static void blk_crypto_fallback_encrypt_bio(struct bio *src_bio)
skcipher_request_set_crypt(ciph_req, &src, &dst, data_unit_size,
iv.bytes);
/* Encrypt each page in the bounce bio */
for (i = 0; i < enc_bio->bi_vcnt; i++) {
struct bio_vec *enc_bvec = &enc_bio->bi_io_vec[i];
struct page *plaintext_page = enc_bvec->bv_page;
struct page *ciphertext_page =
mempool_alloc(blk_crypto_bounce_page_pool, GFP_NOIO);
/*
* Encrypt each page in the source bio. Because the source bio could
* have bio_vecs that span more than a single page, but the encrypted
* bios are limited to a single page per bio_vec, this can generate
* more than a single encrypted bio per source bio.
*/
new_bio:
nr_enc_pages = min(bio_segments(src_bio), BIO_MAX_VECS);
enc_bio = blk_crypto_alloc_enc_bio(src_bio, nr_enc_pages);
enc_idx = 0;
for (;;) {
struct bio_vec src_bv =
bio_iter_iovec(src_bio, src_bio->bi_iter);
struct page *enc_page;
enc_bvec->bv_page = ciphertext_page;
enc_page = mempool_alloc(blk_crypto_bounce_page_pool,
GFP_NOIO);
__bio_add_page(enc_bio, enc_page, src_bv.bv_len,
src_bv.bv_offset);
if (!ciphertext_page) {
src_bio->bi_status = BLK_STS_RESOURCE;
goto out_free_bounce_pages;
}
sg_set_page(&src, src_bv.bv_page, data_unit_size,
src_bv.bv_offset);
sg_set_page(&dst, enc_page, data_unit_size, src_bv.bv_offset);
sg_set_page(&src, plaintext_page, data_unit_size,
enc_bvec->bv_offset);
sg_set_page(&dst, ciphertext_page, data_unit_size,
enc_bvec->bv_offset);
/*
* Increment the index now that the encrypted page is added to
* the bio. This is important for the error unwind path.
*/
enc_idx++;
/* Encrypt each data unit in this page */
for (j = 0; j < enc_bvec->bv_len; j += data_unit_size) {
/*
* Encrypt each data unit in this page.
*/
for (i = 0; i < src_bv.bv_len; i += data_unit_size) {
blk_crypto_dun_to_iv(curr_dun, &iv);
if (crypto_wait_req(crypto_skcipher_encrypt(ciph_req),
&wait)) {
i++;
src_bio->bi_status = BLK_STS_IOERR;
goto out_free_bounce_pages;
bio_io_error(enc_bio);
goto out_free_request;
}
bio_crypt_dun_increment(curr_dun, 1);
src.offset += data_unit_size;
dst.offset += data_unit_size;
}
bio_advance_iter_single(src_bio, &src_bio->bi_iter,
src_bv.bv_len);
if (!src_bio->bi_iter.bi_size)
break;
if (enc_idx == nr_enc_pages) {
/*
* For each additional encrypted bio submitted,
* increment the source bio's remaining count. Each
* encrypted bio's completion handler calls bio_endio on
* the source bio, so this keeps the source bio from
* completing until the last encrypted bio does.
*/
bio_inc_remaining(src_bio);
submit_bio(enc_bio);
goto new_bio;
}
}
enc_bio->bi_private = src_bio;
enc_bio->bi_end_io = blk_crypto_fallback_encrypt_endio;
skcipher_request_free(ciph_req);
blk_crypto_put_keyslot(slot);
submit_bio(enc_bio);
return;
out_free_bounce_pages:
while (i > 0)
mempool_free(enc_bio->bi_io_vec[--i].bv_page,
blk_crypto_bounce_page_pool);
out_free_request:
skcipher_request_free(ciph_req);
out_release_keyslot:
blk_crypto_put_keyslot(slot);
out_put_enc_bio:
bio_uninit(enc_bio);
kfree(enc_bio);
out_endio:
bio_endio(src_bio);
}
/*
@@ -533,7 +504,7 @@ static int blk_crypto_fallback_init(void)
get_random_bytes(blank_key, sizeof(blank_key));
err = bioset_init(&crypto_bio_split, 64, 0, 0);
err = bioset_init(&enc_bio_set, 64, 0, BIOSET_NEED_BVECS);
if (err)
goto out;
@@ -603,7 +574,7 @@ fail_destroy_profile:
fail_free_profile:
kfree(blk_crypto_fallback_profile);
fail_free_bioset:
bioset_exit(&crypto_bio_split);
bioset_exit(&enc_bio_set);
out:
return err;
}