[RFC 2/4] block: relax direct io memory alignment

[Keith Busch]

From: Keith Busch <kbusch at 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.

Signed-off-by: Keith Busch <kbusch at kernel.org>
---
 block/fops.c           | 15 +++++++++------
 fs/direct-io.c         | 11 +++++++----
 fs/iomap/direct-io.c   |  3 ++-
 include/linux/blkdev.h |  5 +++++
 4 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 9f2ecec406b0..a6583bce1e7d 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -62,8 +62,9 @@ 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;
 
 	if (nr_pages <= DIO_INLINE_BIO_VECS)
@@ -193,8 +194,9 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	loff_t pos = iocb->ki_pos;
 	int ret = 0;
 
-	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;
 
 	bio = bio_alloc_kiocb(iocb, bdev, nr_pages, opf, &blkdev_dio_pool);
@@ -316,8 +318,9 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 	loff_t pos = iocb->ki_pos;
 	int ret = 0;
 
-	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;
 
 	bio = bio_alloc_kiocb(iocb, bdev, nr_pages, opf, &blkdev_dio_pool);
diff --git a/fs/direct-io.c b/fs/direct-io.c
index aef06e607b40..b3d249d7d91d 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1132,7 +1132,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	struct dio_submit sdio = { 0, };
 	struct buffer_head map_bh = { 0, };
 	struct blk_plug plug;
-	unsigned long align = offset | iov_iter_alignment(iter);
+	unsigned long align = iov_iter_alignment(iter);
 
 	/*
 	 * Avoid references to bdev if not absolutely needed to give
@@ -1166,11 +1166,14 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		goto fail_dio;
 	}
 
-	if (align & blocksize_mask) {
-		if (bdev)
+	if ((offset | align) & blocksize_mask) {
+		if (bdev) {
 			blkbits = blksize_bits(bdev_logical_block_size(bdev));
+			if (align & bdev_dma_alignment(bdev))
+				goto fail_dio;
+		}
 		blocksize_mask = (1 << blkbits) - 1;
-		if (align & blocksize_mask)
+		if ((offset | count) & blocksize_mask)
 			goto fail_dio;
 	}
 
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index b08f5dc31780..c73b050b7026 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -243,7 +243,8 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 	size_t copied = 0;
 	size_t orig_count;
 
-	if ((pos | length | align) & ((1 << blkbits) - 1))
+	if ((pos | length) & ((1 << blkbits) - 1) ||
+	    align & bdev_dma_alignment(iomap->bdev))
 		return -EINVAL;
 
 	if (iomap->type == IOMAP_UNWRITTEN) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 60d016138997..dba6d411fc1e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1378,6 +1378,11 @@ static inline int queue_dma_alignment(const struct request_queue *q)
 	return q ? q->dma_alignment : 511;
 }
 
+static inline unsigned int bdev_dma_alignment(struct block_device *bdev)
+{
+	return queue_dma_alignment(bdev_get_queue(bdev));
+}
+
 static inline int blk_rq_aligned(struct request_queue *q, unsigned long addr,
 				 unsigned int len)
 {
-- 
2.30.2