blk-crypto: optimize bio splitting in blk_crypto_fallback_encrypt_bio

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>

diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
index cc9e90be23b7fb1f4dc5ba4959a9413374b8ec9c..4ec7da3422805bb34b807fa3462eb46cef351c24 100644 (file)
--- a/block/blk-crypto-fallback.c
+++ b/block/blk-crypto-fallback.c
@@ -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);
-
-               enc_bvec->bv_page = ciphertext_page;
-
-               if (!ciphertext_page) {
-                       src_bio->bi_status = BLK_STS_RESOURCE;
-                       goto out_free_bounce_pages;
-               }
-
-               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);
-
-               /* Encrypt each data unit in this page */
-               for (j = 0; j < enc_bvec->bv_len; j += data_unit_size) {
+       /*
+        * 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_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);
+
+               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);
+
+               /*
+                * 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 (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;
 }