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

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Message-ID: <aLGehMVsTEXrP_R5@kbusch-mbp>
Date: Fri, 29 Aug 2025 06:35:16 -0600
From: Keith Busch <kbusch@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
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 08:45:42PM -0300, Jason Gunthorpe wrote:
> 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.

Sure, I can get all that added in for the real patch.
 
> 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?) ??

We have available bits in the bio_integrity_payload bip_flags, so that
sounds doable. I think we'll need to rearrange some things so we can
reuse the important code for data and metadata mapping/unmapping, but
doesn't look too bad. I'll get started on that.