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Date: Thu, 28 Aug 2025 13:10:32 -0600
From: Keith Busch <kbusch@kernel.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Leon Romanovsky <leon@kernel.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Abdiel Janulgue <abdiel.janulgue@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Alex Gaynor <alex.gaynor@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>, Danilo Krummrich <dakr@kernel.org>,
	iommu@lists.linux.dev, Jason Wang <jasowang@redhat.com>,
	Jens Axboe <axboe@kernel.dk>, Joerg Roedel <joro@8bytes.org>,
	Jonathan Corbet <corbet@lwn.net>, Juergen Gross <jgross@suse.com>,
	kasan-dev@googlegroups.com, linux-block@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-nvme@lists.infradead.org,
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	Madhavan Srinivasan <maddy@linux.ibm.com>,
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	Michael Ellerman <mpe@ellerman.id.au>,
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	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v4 15/16] block-dma: properly take MMIO path
Message-ID: <aLCpqI-VQ7KeB6DL@kbusch-mbp>
References: <cover.1755624249.git.leon@kernel.org>
 <642dbeb7aa94257eaea71ec63c06e3f939270023.1755624249.git.leon@kernel.org>
 <aLBzeMNT3WOrjprC@kbusch-mbp>
 <20250828165427.GB10073@unreal>
 <aLCOqIaoaKUEOdeh@kbusch-mbp>
 <20250828184115.GE7333@nvidia.com>
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In-Reply-To: <20250828184115.GE7333@nvidia.com>

On Thu, Aug 28, 2025 at 03:41:15PM -0300, Jason Gunthorpe wrote:
> On Thu, Aug 28, 2025 at 11:15:20AM -0600, Keith Busch wrote:
> > 
> > I don't think that was ever the case. Metadata is allocated
> > independently of the data payload, usually by the kernel in
> > bio_integrity_prep() just before dispatching the request. The bio may
> > have a p2p data payload, but the integrity metadata is just a kmalloc
> > buf in that path.
> 
> Then you should do two dma mapping operations today, that is how the
> API was built. You shouldn't mix P2P and non P2P within a single
> operation right now..

Data and metadata are mapped as separate operations. They're just
different parts of one blk-mq request.