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

[Christian Borntraeger]

CCing Stefan, Jan.

Below is necessary (in dasd-eckd.c) to make kvm boot working again (and this seems to be the right thing anyway).

Am 29.06.22 um 21:07 schrieb Keith Busch:
> On Wed, Jun 29, 2022 at 02:04:47PM -0400, Eric Farman wrote:
>> s390 dasd
>>
>> This made me think to change my rootfs, and of course the problem goes
>> away once on something like a SCSI volume.
>>
>> So crawling through the dasd (instead of virtio) driver and I finally
>> find the point where a change to dma_alignment (which you mentioned
>> earlier) would actually fit.
>>
>> Such a change fixes this for me, so I'll run it by our DASD guys.
>> Thanks for your help and patience.
> 
> I'm assuming there's some driver or device requirement that's making this
> necessary. Is the below driver change what you're looking for? If so, I think
> you might want this regardless of this direct-io patch just because other
> interfaces like blk_rq_map_user_iov() and blk_rq_aligned() align to it.
> 
> ---
> diff --git a/drivers/s390/block/dasd_fba.c b/drivers/s390/block/dasd_fba.c
> index 60be7f7bf2d1..5c79fb02cded 100644
> --- a/drivers/s390/block/dasd_fba.c
> +++ b/drivers/s390/block/dasd_fba.c
> @@ -780,6 +780,7 @@ static void dasd_fba_setup_blk_queue(struct dasd_block *block)
>   	/* With page sized segments each segment can be translated into one idaw/tidaw */
>   	blk_queue_max_segment_size(q, PAGE_SIZE);
>   	blk_queue_segment_boundary(q, PAGE_SIZE - 1);
> +	blk_queue_dma_alignment(q, PAGE_SIZE - 1);
>   
>   	q->limits.discard_granularity = logical_block_size;
>   
> --