linux-kernel - Re: [RFC v2 04/11] block: introduce dma token backed bio type

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aTFm5dHzH3IRID8o@infradead.org>
Date: Thu, 4 Dec 2025 02:48:05 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: linux-block@...r.kernel.org, io-uring@...r.kernel.org,
	Vishal Verma <vishal1.verma@...el.com>, tushar.gohad@...el.com,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [RFC v2 04/11] block: introduce dma token backed bio type

> diff --git a/block/bio.c b/block/bio.c
> index 7b13bdf72de0..8793f1ee559d 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -843,6 +843,11 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
>  		bio_clone_blkg_association(bio, bio_src);
>  	}
>  
> +	if (bio_flagged(bio_src, BIO_DMA_TOKEN)) {
> +		bio->dma_token = bio_src->dma_token;
> +		bio_set_flag(bio, BIO_DMA_TOKEN);
> +	}

Historically __bio_clone itself does not clone the payload, just the
bio.  But we got rid of the callers that want to clone a bio but not
the payload long time ago.

I'd suggest a prep patch that moves assigning bi_io_vec from
bio_alloc_clone and bio_init_clone into __bio_clone, and given that they
are the same field that'll take carw of the dma token as well.
Alternatively do it in an if/else that the compiler will hopefully
optimize away.

> @@ -1349,6 +1366,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
>  		bio_iov_bvec_set(bio, iter);
>  		iov_iter_advance(iter, bio->bi_iter.bi_size);
>  		return 0;
> +	} else if (iov_iter_is_dma_token(iter)) {

No else after an return please.

> +++ b/block/blk-merge.c
> @@ -328,6 +328,29 @@ int bio_split_io_at(struct bio *bio, const struct queue_limits *lim,
>  	unsigned nsegs = 0, bytes = 0, gaps = 0;
>  	struct bvec_iter iter;
>  
> +	if (bio_flagged(bio, BIO_DMA_TOKEN)) {

Please split the dmabuf logic into a self-contained
helper here.

> +		int offset = offset_in_page(bio->bi_iter.bi_bvec_done);
> +
> +		nsegs = ALIGN(bio->bi_iter.bi_size + offset, PAGE_SIZE);
> +		nsegs >>= PAGE_SHIFT;

Why are we hardcoding PAGE_SIZE based "segments" here?

> +
> +		if (offset & lim->dma_alignment || bytes & len_align_mask)
> +			return -EINVAL;
> +
> +		if (bio->bi_iter.bi_size > max_bytes) {
> +			bytes = max_bytes;
> +			nsegs = (bytes + offset) >> PAGE_SHIFT;
> +			goto split;
> +		} else if (nsegs > lim->max_segments) {

No else after a goto either.