[PATCHv4 2/2] dm-crypt: allow unaligned bio_vecs for direct io

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Many storage devices can handle DMA for data that is not aligned to the
logical block size. The block and filesystem layers have introduced
updates to allow that kind of memory alignment flexibility when
possible.

dm-crypt, however, currently constrains itself to aligned memory because
it sends a single scatterlist element for the in/out list to the encrypt
and decrypt algorithms. This forces applications that have unaligned
data to copy through a bounce buffer, increasing CPU and memory
utilization.

Use multiple scatterlist elements to relax the memory alignment
requirement. To keep this simple, this more flexible constraint is
enabled only for certain encryption and initialization vector types,
specifically the ones that don't have additional use for the request
scatterlist elements beyond pointing to user data.

In the unlikely case where the incoming bio uses a highly fragmented
vector, the four inline scatterlist elements may not be enough, so
allocate a temporary scatterlist when needed, falling back to a mempool
for the in and out buffers to guarantee forward progress if the initial
allocation fails.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/md/dm-crypt.c | 147 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 127 insertions(+), 20 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 608b617fb817f..19e8101580d1a 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -101,6 +101,10 @@ struct dm_crypt_request {
 	struct scatterlist sg_in[4];
 	struct scatterlist sg_out[4];
 	u64 iv_sector;
+	struct scatterlist *__sg_in;
+	struct scatterlist *__sg_out;
+	bool sg_in_pooled;
+	bool sg_out_pooled;
 };
 
 struct crypt_config;
@@ -216,6 +220,9 @@ struct crypt_config {
 	unsigned int key_extra_size; /* additional keys length */
 	unsigned int key_mac_size;   /* MAC key size for authenc(...) */
 
+	unsigned int io_alignment;
+	mempool_t sg_in_pool;
+	mempool_t sg_out_pool;
 	unsigned int integrity_tag_size;
 	unsigned int integrity_iv_size;
 	unsigned int used_tag_size;
@@ -1349,22 +1356,89 @@ static int crypt_convert_block_aead(struct crypt_config *cc,
 	return r;
 }
 
+static void crypt_free_sg(struct scatterlist *sg, struct scatterlist *inline_sg,
+			  mempool_t *pool, bool from_pool)
+{
+	if (sg == inline_sg)
+		return;
+	if (from_pool)
+		mempool_free(sg, pool);
+	else
+		kfree(sg);
+}
+
+static void crypt_free_sgls(struct crypt_config *cc,
+			    struct dm_crypt_request *dmreq)
+{
+	crypt_free_sg(dmreq->__sg_in, dmreq->sg_in,
+		      &cc->sg_in_pool, dmreq->sg_in_pooled);
+	crypt_free_sg(dmreq->__sg_out, dmreq->sg_out,
+		      &cc->sg_out_pool, dmreq->sg_out_pooled);
+	dmreq->__sg_in = NULL;
+	dmreq->__sg_out = NULL;
+}
+
+static int crypt_build_sgl(struct crypt_config *cc, struct scatterlist **psg,
+			   struct bvec_iter *iter, struct bio *bio,
+			   int max_segs, mempool_t *pool, bool *pooled)
+{
+	unsigned int bytes = cc->sector_size;
+	struct scatterlist *sg = *psg;
+	struct bvec_iter tmp = *iter;
+	int segs, i = 0;
+
+	*pooled = false;
+	bio_advance_iter(bio, &tmp, bytes);
+	segs = tmp.bi_idx - iter->bi_idx + !!tmp.bi_bvec_done;
+	if (segs > max_segs) {
+		if (unlikely(segs > BIO_MAX_VECS))
+			return -EIO;
+		sg = kmalloc_array(segs, sizeof(struct scatterlist),
+				   GFP_NOWAIT | __GFP_NOMEMALLOC);
+		if (!sg) {
+			sg = mempool_alloc(pool, GFP_NOIO);
+			*pooled = true;
+		}
+	}
+
+	sg_init_table(sg, segs);
+	do {
+		struct bio_vec bv = mp_bvec_iter_bvec(bio->bi_io_vec, *iter);
+		int len = min(bytes, bv.bv_len);
+
+		/* Reject unexpected unaligned bio. */
+		if (unlikely((len | bv.bv_offset) & cc->io_alignment))
+			goto error;
+
+		sg_set_page(&sg[i++], bv.bv_page, len, bv.bv_offset);
+		bio_advance_iter_single(bio, iter, len);
+		bytes -= len;
+	} while (bytes);
+
+	if (WARN_ON_ONCE(i != segs))
+		goto error;
+	*psg = sg;
+	return 0;
+error:
+	if (sg != *psg) {
+		if (*pooled)
+			mempool_free(sg, pool);
+		else
+			kfree(sg);
+	}
+	return -EIO;
+}
+
 static int crypt_convert_block_skcipher(struct crypt_config *cc,
 					struct convert_context *ctx,
 					struct skcipher_request *req,
 					unsigned int tag_offset)
 {
-	struct bio_vec bv_in = bio_iter_iovec(ctx->bio_in, ctx->iter_in);
-	struct bio_vec bv_out = bio_iter_iovec(ctx->bio_out, ctx->iter_out);
 	struct scatterlist *sg_in, *sg_out;
 	struct dm_crypt_request *dmreq;
 	u8 *iv, *org_iv, *tag_iv;
 	__le64 *sector;
-	int r = 0;
-
-	/* Reject unexpected unaligned bio. */
-	if (unlikely(bv_in.bv_len & (cc->sector_size - 1)))
-		return -EIO;
+	int r;
 
 	dmreq = dmreq_of_req(cc, req);
 	dmreq->iv_sector = ctx->cc_sector;
@@ -1381,15 +1455,23 @@ static int crypt_convert_block_skcipher(struct crypt_config *cc,
 	sector = org_sector_of_dmreq(cc, dmreq);
 	*sector = cpu_to_le64(ctx->cc_sector - cc->iv_offset);
 
-	/* For skcipher we use only the first sg item */
-	sg_in  = &dmreq->sg_in[0];
-	sg_out = &dmreq->sg_out[0];
+	dmreq->__sg_in = &dmreq->sg_in[0];
+	dmreq->__sg_out = &dmreq->sg_out[0];
+
+	r = crypt_build_sgl(cc, &dmreq->__sg_in, &ctx->iter_in, ctx->bio_in,
+			    ARRAY_SIZE(dmreq->sg_in), &cc->sg_in_pool,
+			    &dmreq->sg_in_pooled);
+	if (r < 0)
+		return r;
 
-	sg_init_table(sg_in, 1);
-	sg_set_page(sg_in, bv_in.bv_page, cc->sector_size, bv_in.bv_offset);
+	r = crypt_build_sgl(cc, &dmreq->__sg_out, &ctx->iter_out, ctx->bio_out,
+			    ARRAY_SIZE(dmreq->sg_out), &cc->sg_out_pool,
+			    &dmreq->sg_out_pooled);
+	if (r < 0)
+		goto out;
 
-	sg_init_table(sg_out, 1);
-	sg_set_page(sg_out, bv_out.bv_page, cc->sector_size, bv_out.bv_offset);
+	sg_in = dmreq->__sg_in;
+	sg_out = dmreq->__sg_out;
 
 	if (cc->iv_gen_ops) {
 		/* For READs use IV stored in integrity metadata */
@@ -1398,7 +1480,7 @@ static int crypt_convert_block_skcipher(struct crypt_config *cc,
 		} else {
 			r = cc->iv_gen_ops->generator(cc, org_iv, dmreq);
 			if (r < 0)
-				return r;
+				goto out;
 			/* Data can be already preprocessed in generator */
 			if (test_bit(CRYPT_ENCRYPT_PREPROCESS, &cc->cipher_flags))
 				sg_in = sg_out;
@@ -1420,8 +1502,9 @@ static int crypt_convert_block_skcipher(struct crypt_config *cc,
 	if (!r && cc->iv_gen_ops && cc->iv_gen_ops->post)
 		cc->iv_gen_ops->post(cc, org_iv, dmreq);
 
-	bio_advance_iter(ctx->bio_in, &ctx->iter_in, cc->sector_size);
-	bio_advance_iter(ctx->bio_out, &ctx->iter_out, cc->sector_size);
+out:
+	if (r != -EINPROGRESS && r != -EBUSY)
+		crypt_free_sgls(cc, dmreq);
 
 	return r;
 }
@@ -1487,7 +1570,9 @@ static void crypt_free_req_skcipher(struct crypt_config *cc,
 				    struct skcipher_request *req, struct bio *base_bio)
 {
 	struct dm_crypt_io *io = dm_per_bio_data(base_bio, cc->per_bio_data_size);
+	struct dm_crypt_request *dmreq = dmreq_of_req(cc, req);
 
+	crypt_free_sgls(cc, dmreq);
 	if ((struct skcipher_request *)(io + 1) != req)
 		mempool_free(req, &cc->req_pool);
 }
@@ -2717,6 +2802,8 @@ static void crypt_dtr(struct dm_target *ti)
 
 	mempool_exit(&cc->page_pool);
 	mempool_exit(&cc->req_pool);
+	mempool_exit(&cc->sg_in_pool);
+	mempool_exit(&cc->sg_out_pool);
 	mempool_exit(&cc->tag_pool);
 
 	WARN_ON(percpu_counter_sum(&cc->n_allocated_pages) != 0);
@@ -2751,9 +2838,10 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 {
 	struct crypt_config *cc = ti->private;
 
-	if (crypt_integrity_aead(cc))
+	if (crypt_integrity_aead(cc)) {
 		cc->iv_size = crypto_aead_ivsize(any_tfm_aead(cc));
-	else
+		cc->io_alignment = cc->sector_size - 1;
+	} else
 		cc->iv_size = crypto_skcipher_ivsize(any_tfm(cc));
 
 	if (cc->iv_size)
@@ -2789,6 +2877,7 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 		if (cc->key_extra_size > ELEPHANT_MAX_KEY_SIZE)
 			return -EINVAL;
 		set_bit(CRYPT_ENCRYPT_PREPROCESS, &cc->cipher_flags);
+		cc->io_alignment = cc->sector_size - 1;
 	} else if (strcmp(ivmode, "lmk") == 0) {
 		cc->iv_gen_ops = &crypt_iv_lmk_ops;
 		/*
@@ -2801,10 +2890,12 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 			cc->key_parts++;
 			cc->key_extra_size = cc->key_size / cc->key_parts;
 		}
+		cc->io_alignment = cc->sector_size - 1;
 	} else if (strcmp(ivmode, "tcw") == 0) {
 		cc->iv_gen_ops = &crypt_iv_tcw_ops;
 		cc->key_parts += 2; /* IV + whitening */
 		cc->key_extra_size = cc->iv_size + TCW_WHITENING_SIZE;
+		cc->io_alignment = cc->sector_size - 1;
 	} else if (strcmp(ivmode, "random") == 0) {
 		cc->iv_gen_ops = &crypt_iv_random_ops;
 		/* Need storage space in integrity fields. */
@@ -3271,6 +3362,20 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		ALIGN(sizeof(struct dm_crypt_io) + cc->dmreq_start + additional_req_size,
 		      ARCH_DMA_MINALIGN);
 
+	ret = mempool_init_kmalloc_pool(&cc->sg_in_pool, 1,
+			BIO_MAX_VECS * sizeof(struct scatterlist));
+	if (ret) {
+		ti->error = "Cannot allocate crypt scatterlist mempool";
+		goto bad;
+	}
+
+	ret = mempool_init_kmalloc_pool(&cc->sg_out_pool, 1,
+			BIO_MAX_VECS * sizeof(struct scatterlist));
+	if (ret) {
+		ti->error = "Cannot allocate crypt scatterlist mempool";
+		goto bad;
+	}
+
 	ret = mempool_init(&cc->page_pool, BIO_MAX_VECS, crypt_page_alloc, crypt_page_free, cc);
 	if (ret) {
 		ti->error = "Cannot allocate page mempool";
@@ -3680,7 +3785,9 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	struct crypt_config *cc = ti->private;
 
 	dm_stack_bs_limits(limits, cc->sector_size);
-	limits->dma_alignment = limits->logical_block_size - 1;
+	limits->dma_alignment = max(bdev_dma_alignment(cc->dev->bdev),
+				    cc->io_alignment);
+	cc->io_alignment = limits->dma_alignment;
 
 	/*
 	 * For zoned dm-crypt targets, there will be no internal splitting of
-- 
2.52.0