linux-kernel - Re: [RFC v2 01/11] file: add callback for pre-mapping dmabuf

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] [day] [month] [year] [list]

Message-ID: <20260109055852.GA5063@lst.de>
Date: Fri, 9 Jan 2026 06:58:52 +0100
From: Christoph Hellwig <hch@....de>
To: Ming Lei <ming.lei@...hat.com>
Cc: Christoph Hellwig <hch@....de>,
	Christian König <christian.koenig@....com>,
	Pavel Begunkov <asml.silence@...il.com>,
	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>,
	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>,
	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 01/11] file: add callback for pre-mapping dmabuf

On Fri, Jan 09, 2026 at 10:10:57AM +0800, Ming Lei wrote:
> On Thu, Jan 08, 2026 at 11:17:03AM +0100, Christoph Hellwig wrote:
> > On Thu, Jan 08, 2026 at 10:19:18AM +0800, Ming Lei wrote:
> > > > The feature is in no way nvme specific.  nvme is just the initial
> > > > underlying driver.  It makes total sense to support this for any high
> > > > performance block device, and to pass it through file systems.
> > > 
> > > But why does FS care the dma buffer attachment? Since high performance
> > > host controller is exactly the dma buffer attachment point.
> > 
> > I can't parse what you're trying to say here.
> 
> dma buffer attachment is simply none of FS's business.

The file systems should indeed never do a dma buffer attachment itself,
but that's not the point.

> > But even when not stacking, the registration still needs to go
> > through the file system even for a single device, never mind multiple
> > controlled by the file system.
> 
> dma_buf can have multiple importers, so why does it have to go through FS for
> single device only?
>
> If the registered buffer is attached to single device before going
> through FS, it can not support stacking block device, and it can't or not
> easily to use for multiple block device, no matter if they are behind same
> host controller or multiple.

Because the file system, or the file_operations instance to be more
specific, is the only entity that known what block device(s) or other DMA
capable device(s) like (R)NIC a file maps to.