On Thu, Jul 10, 2025 at 12:12:29PM -0400, Mike Snitzer wrote:
> All said, in practice I haven't had any issues with this patch. But
> it could just be I don't have the stars aligned to test the case that
> might have problems. If you know of such a case I'd welcome
> suggestions.
This is something I threw together that appears to be successful with
NVMe through raw block direct-io. This will defer catching an invalid io
vector to much later in the block stack, which should be okay, and
removes one of the vector walks in the fast path, so that's a bonus.
While this is testing okay with NVMe so far, I haven't tested any more
complicated setups yet, and I probably need to get filesystems using
this relaxed limit too.
---
diff --git a/block/bio.c b/block/bio.c
index 92c512e876c8d..634b2031c4829 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1227,13 +1227,6 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
if (bio->bi_bdev && blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
extraction_flags |= ITER_ALLOW_P2PDMA;
- /*
- * 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.
- */
size = iov_iter_extract_pages(iter, &pages,
UINT_MAX - bio->bi_iter.bi_size,
nr_pages, extraction_flags, &offset);
@@ -1241,18 +1234,6 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
return size ? size : -EFAULT;
nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE);
-
- if (bio->bi_bdev) {
- size_t trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1);
- iov_iter_revert(iter, trim);
- size -= trim;
- }
-
- if (unlikely(!size)) {
- ret = -EFAULT;
- goto out;
- }
-
for (left = size, i = 0; left > 0; left -= len, i += num_pages) {
struct page *page = pages[i];
struct folio *folio = page_folio(page);
@@ -1297,6 +1278,23 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
return ret;
}
+static int bio_align_to_bs(struct bio *bio, struct iov_iter *iter)
+{
+ unsigned int mask = bdev_logical_block_size(bio->bi_bdev) - 1;
+ unsigned int total = bio->bi_iter.bi_size;
+ size_t trim = total & mask;
+
+ if (!trim)
+ return 0;
+
+ /* FIXME: might be leaking pages */
+ bio_revert(bio, trim);
+ iov_iter_revert(iter, trim);
+ if (total == trim)
+ return -EFAULT;
+ return 0;
+}
+
/**
* bio_iov_iter_get_pages - add user or kernel pages to a bio
* @bio: bio to add pages to
@@ -1327,7 +1325,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
if (iov_iter_is_bvec(iter)) {
bio_iov_bvec_set(bio, iter);
iov_iter_advance(iter, bio->bi_iter.bi_size);
- return 0;
+ return bio_align_to_bs(bio, iter);
}
if (iov_iter_extract_will_pin(iter))
@@ -1336,6 +1334,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
ret = __bio_iov_iter_get_pages(bio, iter);
} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));
+ ret = bio_align_to_bs(bio, iter);
return bio->bi_vcnt ? 0 : ret;
}
EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 70d704615be52..a3acfef8eb81d 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -298,6 +298,9 @@ int bio_split_rw_at(struct bio *bio, const struct queue_limits *lim,
unsigned nsegs = 0, bytes = 0;
bio_for_each_bvec(bv, bio, iter) {
+ if (bv.bv_offset & lim->dma_alignment)
+ return -EFAULT;
+
/*
* If the queue doesn't support SG gaps and adding this
* offset would create a gap, disallow it.
@@ -341,6 +344,8 @@ int bio_split_rw_at(struct bio *bio, const struct queue_limits *lim,
* we do not use the full hardware limits.
*/
bytes = ALIGN_DOWN(bytes, bio_split_alignment(bio, lim));
+ if (!bytes)
+ return -EFAULT;
/*
* Bio splitting may cause subtle trouble such as hang when doing sync
diff --git a/block/fops.c b/block/fops.c
index 82451ac8ff25d..820902cf10730 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -38,8 +38,8 @@ static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
static bool blkdev_dio_invalid(struct block_device *bdev, struct kiocb *iocb,
struct iov_iter *iter)
{
- return iocb->ki_pos & (bdev_logical_block_size(bdev) - 1) ||
- !bdev_iter_is_aligned(bdev, iter);
+ return (iocb->ki_pos | iov_iter_count(iter)) &
+ (bdev_logical_block_size(bdev) - 1);
}
#define DIO_INLINE_BIO_VECS 4
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 46ffac5caab78..d3ddf78d1f35e 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -169,6 +169,22 @@ static inline void bio_advance(struct bio *bio, unsigned int nbytes)
#define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
+static inline void bio_revert(struct bio *bio, unsigned int nbytes)
+{
+ bio->bi_iter.bi_size -= nbytes;
+
+ while (nbytes) {
+ struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
+
+ if (nbytes < bv->bv_len) {
+ bv->bv_len -= nbytes;
+ return;
+ }
+ bio->bi_vcnt--;
+ nbytes -= bv->bv_len;
+ }
+}
+
static inline unsigned bio_segments(struct bio *bio)
{
unsigned segs = 0;
--
