Re: [PATCH v7 1/8] block: ensure bios are not split in middle of crypto data unit

Eric Biggers
2020-11-17T23:31:57Z

On Tue, Nov 17, 2020 at 02:07:01PM +0000, Satya Tangirala wrote:
> Introduce blk_crypto_bio_sectors_alignment() that returns the required
> alignment for the number of sectors in a bio. Any bio split must ensure
> that the number of sectors in the resulting bios is aligned to that
> returned value. This patch also updates __blk_queue_split(),
> __blk_queue_bounce() and blk_crypto_split_bio_if_needed() to respect
> blk_crypto_bio_sectors_alignment() when splitting bios.
>
> Signed-off-by: Satya Tangirala <satyat@google.com>
> ---
> block/bio.c | 1 +
> block/blk-crypto-fallback.c | 10 ++--
> block/blk-crypto-internal.h | 18 +++++++
> block/blk-merge.c | 96 ++++++++++++++++++++++++++++++++-----
> block/blk-mq.c | 3 ++
> block/bounce.c | 4 ++
> 6 files changed, 117 insertions(+), 15 deletions(-)
>

I feel like this should be split into multiple patches: one patch that
introduces blk_crypto_bio_sectors_alignment(), and a patch for each place that
needs to take blk_crypto_bio_sectors_alignment() into account.

It would also help to give a real-world example of why support for
data_unit_size > logical_block_size is needed. E.g. ext4 or f2fs encryption
with a 4096-byte filesystem block size, using eMMC inline encryption hardware
that has logical_block_size=512.

Also, is this needed even without the fscrypt direct I/O support? If so, it
should be sent out separately.

> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index bcf5e4580603..f34dda7132f9 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -149,13 +149,15 @@ static inline unsigned get_max_io_size(struct request_queue *q,
> unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
> unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
> unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
> + unsigned int bio_sectors_alignment =
> + blk_crypto_bio_sectors_alignment(bio);
>
> max_sectors += start_offset;
> max_sectors &= ~(pbs - 1);
> - if (max_sectors > start_offset)
> - return max_sectors - start_offset;
> + if (max_sectors - start_offset >= bio_sectors_alignment)
> + return round_down(max_sectors - start_offset, bio_sectors_alignment);
>
> - return sectors & ~(lbs - 1);
> + return round_down(sectors & ~(lbs - 1), bio_sectors_alignment);
> }

'max_sectors - start_offset >= bio_sectors_alignment' looks wrong, as
'max_sectors - start_offset' underflows if 'max_sectors < start_offset'.

Maybe consider something like the below?

static inline unsigned get_max_io_size(struct request_queue *q,
struct bio *bio)
{
unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
sector_t pb_aligned_sector =
round_down(bio->bi_iter.bi_sector + sectors, pbs);

lbs = max(lbs, blk_crypto_bio_sectors_alignment(bio));

if (pb_aligned_sector >= bio->bi_iter.bi_sector + lbs)
sectors = pb_aligned_sector - bio->bi_iter.bi_sector;

return round_down(sectors, lbs);
}

Maybe it would be useful to have a helper function bio_required_alignment() that
returns the crypto data unit size if the bio has an encryption context, and the
logical block size if it doesn't?

>
> static inline unsigned get_max_segment_size(const struct request_queue *q,
> @@ -174,6 +176,41 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
> (unsigned long)queue_max_segment_size(q));
> }
>
> +/**
> + * update_aligned_sectors_and_segs() - Ensures that *@aligned_sectors is aligned
> + * to @bio_sectors_alignment, and that
> + * *@aligned_segs is the value of nsegs
> + * when sectors reached/first exceeded that
> + * value of *@aligned_sectors.
> + *
> + * @nsegs: [in] The current number of segs
> + * @sectors: [in] The current number of sectors
> + * @aligned_segs: [in,out] The number of segments that make up @aligned_sectors
> + * @aligned_sectors: [in,out] The largest number of sectors <= @sectors that is
> + * aligned to @sectors
> + * @bio_sectors_alignment: [in] The alignment requirement for the number of
> + * sectors
> + *
> + * Updates *@aligned_sectors to the largest number <= @sectors that is also a
> + * multiple of @bio_sectors_alignment. This is done by updating *@aligned_sectors
> + * whenever @sectors is at least @bio_sectors_alignment more than
> + * *@aligned_sectors, since that means we can increment *@aligned_sectors while
> + * still keeping it aligned to @bio_sectors_alignment and also keeping it <=
> + * @sectors. *@aligned_segs is updated to the value of nsegs when @sectors first
> + * reaches/exceeds any value that causes *@aligned_sectors to be updated.
> + */
> +static inline void update_aligned_sectors_and_segs(const unsigned int nsegs,
> + const unsigned int sectors,
> + unsigned int *aligned_segs,
> + unsigned int *aligned_sectors,
> + const unsigned int bio_sectors_alignment)
> +{
> + if (sectors - *aligned_sectors < bio_sectors_alignment)
> + return;
> + *aligned_sectors = round_down(sectors, bio_sectors_alignment);
> + *aligned_segs = nsegs;
> +}
> +
> /**
> * bvec_split_segs - verify whether or not a bvec should be split in the middle
> * @q: [in] request queue associated with the bio associated with @bv
> @@ -195,9 +232,12 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
> * the block driver.
> */
> static bool bvec_split_segs(const struct request_queue *q,
> - const struct bio_vec *bv, unsigned *nsegs,
> - unsigned *sectors, unsigned max_segs,
> - unsigned max_sectors)
> + const struct bio_vec *bv, unsigned int *nsegs,
> + unsigned int *sectors, unsigned int *aligned_segs,
> + unsigned int *aligned_sectors,
> + unsigned int bio_sectors_alignment,
> + unsigned int max_segs,
> + unsigned int max_sectors)
> {
> unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
> unsigned len = min(bv->bv_len, max_len);
> @@ -211,6 +251,11 @@ static bool bvec_split_segs(const struct request_queue *q,
>
> (*nsegs)++;
> total_len += seg_size;
> + update_aligned_sectors_and_segs(*nsegs,
> + *sectors + (total_len >> 9),
> + aligned_segs,
> + aligned_sectors,
> + bio_sectors_alignment);
> len -= seg_size;
>
> if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
> @@ -235,6 +280,8 @@ static bool bvec_split_segs(const struct request_queue *q,
> * following is guaranteed for the cloned bio:
> * - That it has at most get_max_io_size(@q, @bio) sectors.
> * - That it has at most queue_max_segments(@q) segments.
> + * - That the number of sectors in the returned bio is aligned to
> + * blk_crypto_bio_sectors_alignment(@bio)
> *
> * Except for discard requests the cloned bio will point at the bi_io_vec of
> * the original bio. It is the responsibility of the caller to ensure that the
> @@ -252,6 +299,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
> unsigned nsegs = 0, sectors = 0;
> const unsigned max_sectors = get_max_io_size(q, bio);
> const unsigned max_segs = queue_max_segments(q);
> + const unsigned int bio_sectors_alignment =
> + blk_crypto_bio_sectors_alignment(bio);
> + unsigned int aligned_segs = 0, aligned_sectors = 0;
>
> bio_for_each_bvec(bv, bio, iter) {
> /*
> @@ -266,8 +316,14 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
> bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
> nsegs++;
> sectors += bv.bv_len >> 9;
> - } else if (bvec_split_segs(q, &bv, &nsegs, &sectors, max_segs,
> - max_sectors)) {
> + update_aligned_sectors_and_segs(nsegs, sectors,
> + &aligned_segs,
> + &aligned_sectors,
> + bio_sectors_alignment);
> + } else if (bvec_split_segs(q, &bv, &nsegs, &sectors,
> + &aligned_segs, &aligned_sectors,
> + bio_sectors_alignment, max_segs,
> + max_sectors)) {
> goto split;
> }
>
> @@ -275,11 +331,24 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
> bvprvp = &bvprv;
> }
>
> + /*
> + * The input bio's number of sectors is assumed to be aligned to
> + * bio_sectors_alignment. If that's the case, then this function should
> + * ensure that aligned_segs == nsegs and aligned_sectors == sectors if
> + * the bio is not going to be split.
> + */
> + WARN_ON(aligned_segs != nsegs || aligned_sectors != sectors);
> *segs = nsegs;
> return NULL;
> split:
> - *segs = nsegs;
> - return bio_split(bio, sectors, GFP_NOIO, bs);
> + *segs = aligned_segs;
> + if (WARN_ON(aligned_sectors == 0))
> + goto err;
> + return bio_split(bio, aligned_sectors, GFP_NOIO, bs);
> +err:
> + bio->bi_status = BLK_STS_IOERR;
> + bio_endio(bio);
> + return bio;
> }

This part is pretty complex. Are you sure it's needed? How was alignment to
logical_block_size ensured before?

> diff --git a/block/bounce.c b/block/bounce.c
> index 162a6eee8999..b15224799008 100644
> --- a/block/bounce.c
> +++ b/block/bounce.c
> @@ -295,6 +295,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> bool bounce = false;
> int sectors = 0;
> bool passthrough = bio_is_passthrough(*bio_orig);
> + unsigned int bio_sectors_alignment;
>
> bio_for_each_segment(from, *bio_orig, iter) {
> if (i++ < BIO_MAX_PAGES)
> @@ -305,6 +306,9 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> if (!bounce)
> return;
>
> + bio_sectors_alignment = blk_crypto_bio_sectors_alignment(bio);
> + sectors = round_down(sectors, bio_sectors_alignment);
> +

This can be one line:

sectors = round_down(sectors, blk_crypto_bio_sectors_alignment(bio));

- Eric