On Wed, May 18, 2022 at 06:53:11PM -0700, Eric Biggers wrote: > On Wed, May 18, 2022 at 07:00:39PM -0600, Keith Busch wrote: > > On Wed, May 18, 2022 at 05:14:49PM -0700, Eric Biggers wrote: > > > On Wed, May 18, 2022 at 10:11:31AM -0700, Keith Busch wrote: > > > > diff --git a/block/fops.c b/block/fops.c > > > > index b9b83030e0df..d8537c29602f 100644 > > > > --- a/block/fops.c > > > > +++ b/block/fops.c > > > > @@ -54,8 +54,9 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb, > > > > struct bio bio; > > > > ssize_t ret; > > > > > > > > - 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; > > > > > > The block layer makes a lot of assumptions that bios can be split at any bvec > > > boundary. With this patch, bios whose length isn't a multiple of the logical > > > block size can be generated by splitting, which isn't valid. > > > > How? This patch ensures every segment is block size aligned. > > No, it doesn't. It ensures that the *total* length of each bio is logical block > size aligned. It doesn't ensure that for the individual bvecs. By decreasing > the required memory alignment to below the logical block size, you're allowing > logical blocks to span a page boundary. Whenever the two pages involved aren't > physically contiguous, the data of the block will be split across two bvecs. I'm aware that spanning pages can cause bad splits on the bi_max_vecs condition, but I believe it's well handled here. Unless I'm terribly confused, which is certainly possible, I think you may have missed this part of the patch: @@ -1223,6 +1224,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); + if (size > 0) + size = ALIGN_DOWN(size, queue_logical_block_size(q)); if (unlikely(size <= 0)) return size ? size : -EFAULT;
