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Date: Fri, 31 Oct 2025 10:07:02 +0100
From: Christoph Hellwig <hch@lst.de>
To: Hans Holmberg <hans.holmberg@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
	Keith Busch <kbusch@kernel.org>,
	Damien Le Moal <dlemoal@kernel.org>,
	Johannes Thumshirn <johannes.thumshirn@wdc.com>,
	Christoph Hellwig <hch@lst.de>,
	Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
	Andreas Hindborg <a.hindborg@kernel.org>
Subject: Re: [PATCH v2] null_blk: set dma alignment to logical block size
Message-ID: <20251031090702.GA9335@lst.de>
References: <20251031090209.131536-1-hans.holmberg@wdc.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Oct 31, 2025 at 10:02:09AM +0100, Hans Holmberg wrote:
> This driver assumes that bio vectors are memory aligned to the logical
> block size, so set the queue limit to reflect that.
> 
> Unless we set up the limit based on the logical block size, we will go
> out of page bounds in copy_to_nullb / copy_from_nullb.

Please also add something like:

Apparently this wasn't noticed so far because none of the tests generate
such buffers, but since 851c4c96db00 ("xfs: implement XFS_IOC_DIOINFO in
terms of vfs_getattr"), xfstests generates unaligned I/O, which now lead
to memory corruption when using null_blk.

> Fixes: bf8d08532bc1 ("iomap: add support for dma aligned direct-io")
> Fixes: b1a000d3b8ec ("block: relax direct io memory alignment")
> Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
> ---
> 
> Changes in v2:
> * Added fixes tags from Christoph
> * Added reviewed-bys from Keith and Christoph

I don't actually see the Reviewed-by tags above..