Re: [PATCHv6 11/11] iomap: add support for dma aligned direct-io

[Eric Farman <farman@linux.ibm.com>]

On Fri, 2022-06-10 at 12:58 -0700, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> Use the address alignment requirements from the block_device for
> direct
> io instead of requiring addresses be aligned to the block size.

Hi Keith,

Our s390 PV guests recently started failing to boot from a -next host,
and git blame brought me here.

As near as I have been able to tell, we start tripping up on this code
from patch 9 [1] that gets invoked with this patch:

>	for (k = 0; k < i->nr_segs; k++, skip = 0) {
>		size_t len = i->iov[k].iov_len - skip;
>
>		if (len > size)
>			len = size;
>		if (len & len_mask)
>			return false;

The iovec we're failing on has two segments, one with a len of x200
(and base of x...000) and another with a len of xe00 (and a base of
x...200), while len_mask is of course xfff.

So before I go any further on what we might have broken, do you happen
to have any suggestions what might be going on here, or something I
should try?

Thanks,
Eric

[1] https://lore.kernel.org/r/20220610195830.3574005-9-kbusch@fb.com/

> 
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/direct-io.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 370c3241618a..5d098adba443 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -242,7 +242,6 @@ static loff_t iomap_dio_bio_iter(const struct
> iomap_iter *iter,
>  	struct inode *inode = iter->inode;
>  	unsigned int blkbits =
> blksize_bits(bdev_logical_block_size(iomap->bdev));
>  	unsigned int fs_block_size = i_blocksize(inode), pad;
> -	unsigned int align = iov_iter_alignment(dio->submit.iter);
>  	loff_t length = iomap_length(iter);
>  	loff_t pos = iter->pos;
>  	unsigned int bio_opf;
> @@ -253,7 +252,8 @@ 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) ||
> +	    !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
>  		return -EINVAL;
>  
>  	if (iomap->type == IOMAP_UNWRITTEN) {