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dm-verity: provide dma_alignment limit in io_hints

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Since Linux v6.1, some filesystems support submitting direct I/O that is
aligned to only dma_alignment instead of the logical_block_size
alignment that was required before.  I/O that is not aligned to the
logical_block_size is difficult to handle in device-mapper targets that
do cryptographic processing of data, as it makes the units of data that
are hashed or encrypted possibly be split across pages, creating rarely
used and rarely tested edge cases.

As such, dm-crypt and dm-integrity have already opted out of this by
setting dma_alignment to 'logical_block_size - 1'.

Although dm-verity does have code that handles these cases (or at least
is intended to do so), supporting direct I/O with such a low amount of
alignment is not really useful on dm-verity devices.  So, opt dm-verity
out of it too so that it's not necessary to handle these edge cases.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Eric Biggers 2024-07-02 16:39:51 +02:00 committed by Mikulas Patocka
parent a7ddb3d49d
commit 09d1430896
1 changed files with 8 additions and 0 deletions
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8
drivers/md/dm-verity-target.c
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@ -1023,6 +1023,14 @@ static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits)
limits->physical_block_size = 1 << v->data_dev_block_bits;
blk_limits_io_min(limits, limits->logical_block_size);
/*
* Similar to what dm-crypt does, opt dm-verity out of support for
* direct I/O that is aligned to less than the traditional direct I/O
* alignment requirement of logical_block_size. This prevents dm-verity
* data blocks from crossing pages, eliminating various edge cases.
*/
limits->dma_alignment = limits->logical_block_size - 1;
}
static void verity_dtr(struct dm_target *ti)