On Thu, Sep 18, 2025 at 09:16:42AM -0700, Keith Busch wrote: > From: Keith Busch <[email protected]> > > Most storage devices can handle DMA for data that is not aligned to the > sector block size. The block and filesystem layers have introduced > updates to allow that kind of memory alignment flexibility when > possible.
I'd love to understand what changes in filesystems you're referring to. Because I know for certain that DIO with memory that isn't 'dma_alignment' aligned fails with certainty ontop of XFS. Pretty certain it balks at DIO that isn't logical_block_size aligned ondisk too. > dm-crypt, however, currently constrains itself to aligned memory because > it sends a single scatterlist element for the input ot the encrypt and > decrypt algorithms. This forces applications that have unaligned data to > copy through a bounce buffer, increasing CPU and memory utilization. Even this notion that an application is somehow able to (unwittingly) lean on "unaligned data to copy through a bounce buffer" -- has me asking: where does Keith get these wonderful toys? Anyway, just asking these things because if they were true I wouldn't be needing to add specialized code to NFSD and NFS to handle misaligned DIO. > It appears to be a pretty straight forward thing to modify for skcipher > since there are 3 unused scatterlist elements immediately available. In > practice, that should be enough as the sector granularity of data > generally doesn't straddle more than one page, if at all. > > Signed-off-by: Keith Busch <[email protected]> > --- > drivers/md/dm-crypt.c | 29 +++++++++++++++++++---------- > 1 file changed, 19 insertions(+), 10 deletions(-) > > diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c > index 5ef43231fe77f..f860716b7a5c1 100644 > --- a/drivers/md/dm-crypt.c > +++ b/drivers/md/dm-crypt.c > @@ -1429,18 +1429,14 @@ static int crypt_convert_block_skcipher(struct > crypt_config *cc, > 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); > + unsigned int bytes = cc->sector_size; > 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; > - > dmreq = dmreq_of_req(cc, req); > dmreq->iv_sector = ctx->cc_sector; > if (test_bit(CRYPT_IV_LARGE_SECTORS, &cc->cipher_flags)) > @@ -1457,11 +1453,24 @@ static int crypt_convert_block_skcipher(struct > crypt_config *cc, > *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]; > > - sg_init_table(sg_in, 1); > - sg_set_page(sg_in, bv_in.bv_page, cc->sector_size, bv_in.bv_offset); > + do { > + struct bio_vec bv_in = bio_iter_iovec(ctx->bio_in, > ctx->iter_in); > + int len = min(bytes, bv_in.bv_len); > + > + if (r >= ARRAY_SIZE(dmreq->sg_in)) > + return -EINVAL; > + > + sg_in = &dmreq->sg_in[r++]; > + memset(sg_in, 0, sizeof(*sg_in)); > + sg_set_page(sg_in, bv_in.bv_page, len, bv_in.bv_offset); > + bio_advance_iter_single(ctx->bio_in, &ctx->iter_in, len); > + bytes -= len; > + } while (bytes); > + > + sg_mark_end(sg_in); > + sg_in = dmreq->sg_in[0]; > > sg_init_table(sg_out, 1); > sg_set_page(sg_out, bv_out.bv_page, cc->sector_size, bv_out.bv_offset); > @@ -1495,7 +1504,6 @@ static int crypt_convert_block_skcipher(struct > crypt_config *cc, > if (!r && cc->iv_gen_ops && cc->iv_gen_ops->post) > r = 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); > > return r; > @@ -3750,7 +3758,8 @@ static void crypt_io_hints(struct dm_target *ti, struct > queue_limits *limits) > limits->physical_block_size = > max_t(unsigned int, limits->physical_block_size, > cc->sector_size); > limits->io_min = max_t(unsigned int, limits->io_min, cc->sector_size); > - limits->dma_alignment = limits->logical_block_size - 1; > + if (crypt_integrity_aead(cc)) > + limits->dma_alignment = limits->logical_block_size - 1; > > /* > * For zoned dm-crypt targets, there will be no internal splitting of > -- > 2.47.3 > >
