Re: [PATCHv4 8/9] block: relax direct io memory alignment

Damien Le Moal
2022-05-26T02:03:08Z

On 2022/05/26 10:06, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
>
> Use the address alignment requirements from the hardware for direct io
> instead of requiring addresses be aligned to the block size. User space
> can discover the alignment requirements from the dma_alignment queue
> attribute.
>
> User space can specify any hardware compatible DMA offset for each
> segment, but every segment length is still required to be a multiple of
> the block size.
>
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
> block/bio.c | 12 ++++++++++++
> block/fops.c | 14 +++++++++++---
> 2 files changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 55d2a9c4e312..c492881959d1 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1219,7 +1219,19 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
> pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
>
> + /*
> + * Each segment in the iov is required to be a block size multiple.
> + * However, we may not be able to get the entire segment if it spans
> + * more pages than bi_max_vecs allows, so we have to ALIGN_DOWN the
> + * result to ensure the bio's total size is correct. The remainder of
> + * the iov data will be picked up in the next bio iteration.
> + *
> + * If the result is ever 0, that indicates the iov fails the segment
> + * size requirement and is an error.
> + */
> size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
> + if (size > 0)
> + size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));
> if (unlikely(size <= 0))
> return size ? size : -EFAULT;
>
> diff --git a/block/fops.c b/block/fops.c
> index bd6c2e13a4e3..6ecbccc552b9 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -45,10 +45,10 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb)
> static int blkdev_dio_aligned(struct block_device *bdev, loff_t pos,
> struct iov_iter *iter)
> {
> - if ((pos | iov_iter_alignment(iter)) &
> - (bdev_logical_block_size(bdev) - 1))
> + if ((pos | iov_iter_count(iter)) & (bdev_logical_block_size(bdev) - 1))
> + return -EINVAL;
> + if (iov_iter_alignment(iter) & bdev_dma_alignment(bdev))
> return -EINVAL;
> -
> return 0;
> }
>
> @@ -88,6 +88,10 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
> bio.bi_ioprio = iocb->ki_ioprio;
>
> ret = bio_iov_iter_get_pages(&bio, iter);
> +
> + /* check if iov is not aligned */
> + if (unlikely(!ret && iov_iter_count(iter)))
> + ret = -EINVAL;
> if (unlikely(ret))
> goto out;
> ret = bio.bi_iter.bi_size;
> @@ -333,6 +337,10 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
> bio_iov_bvec_set(bio, iter);
> } else {
> ret = bio_iov_iter_get_pages(bio, iter);
> +
> + /* check if iov is not aligned */
> + if (unlikely(!ret && iov_iter_count(iter)))
> + ret = -EINVAL;
> if (unlikely(ret)) {
> bio_put(bio);
> return ret;

Looks OK to me.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

--
Damien Le Moal
Western Digital Research