linux-kernel - Re: [PATCH v4 15/16] block-dma: properly take MMIO path

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Message-ID: <20250828234542.GK7333@nvidia.com>
Date: Thu, 28 Aug 2025 20:45:42 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Keith Busch <kbusch@...nel.org>
Cc: Leon Romanovsky <leon@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Abdiel Janulgue <abdiel.janulgue@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>,
	iommu@...ts.linux.dev, Jason Wang <jasowang@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	Jonathan Corbet <corbet@....net>, Juergen Gross <jgross@...e.com>,
	kasan-dev@...glegroups.com, linux-block@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-nvme@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, linux-trace-kernel@...r.kernel.org,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org,
	Sagi Grimberg <sagi@...mberg.me>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v4 15/16] block-dma: properly take MMIO path

On Thu, Aug 28, 2025 at 02:54:35PM -0600, Keith Busch wrote:

> In truth though, I hadn't tried p2p metadata before today, and it looks
> like bio_integrity_map_user() is missing the P2P extraction flags to
> make that work. Just added this patch below, now I can set p2p or host
> memory independently for data and integrity payloads:

I think it is a bit more than that, you have to make sure all the meta
data is the same, either all p2p or all cpu and then record this
somehow so the DMA mapping knows what kind it is.

Once that is all done then the above should still be OK, the dma unmap
of the data can follow Leon's new flag and the dma unmap of the
integrity can follow however integrity kept track (in the
bio_integrity_payload perhaps?) ??

Jason