linux-kernel - Re: [PATCH] nvme: map uring_cmd data even if address is 0

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Message-ID: <20250224160430.GB4701@lst.de>
Date: Mon, 24 Feb 2025 17:04:30 +0100
From: Christoph Hellwig <hch@....de>
To: Keith Busch <kbusch@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Xinyu Zhang <xizhang@...estorage.com>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>, Sagi Grimberg <sagi@...mberg.me>,
	Caleb Sander Mateos <csander@...estorage.com>
Subject: Re: [PATCH] nvme: map uring_cmd data even if address is 0

On Mon, Feb 24, 2025 at 07:54:59AM -0700, Keith Busch wrote:
> On Mon, Feb 24, 2025 at 03:33:51PM +0100, Christoph Hellwig wrote:
> > On Thu, Feb 20, 2025 at 04:51:01PM -0700, Xinyu Zhang wrote:
> > > When using kernel registered bvec fixed buffers, the "address" is
> > > actually the offset into the bvec rather than userspace address.
> > > Therefore it can be 0.
> > 
> > How is that actually going to work?  Who is interpreting that address?
> 
> io_import_fixed() treats the address as an offset into its bio_vec.

Ah, yes.  This is in nvme_uring_data and read from the SQE.  I thought
we were further down.