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

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Message-ID: <20250828165427.GB10073@unreal>
Date: Thu, 28 Aug 2025 19:54:27 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Keith Busch <kbusch@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Jason Gunthorpe <jgg@...dia.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 09:19:20AM -0600, Keith Busch wrote:
> On Tue, Aug 19, 2025 at 08:36:59PM +0300, Leon Romanovsky wrote:
> > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> > index 09b99d52fd36..283058bcb5b1 100644
> > --- a/include/linux/blk_types.h
> > +++ b/include/linux/blk_types.h
> > @@ -387,6 +387,7 @@ enum req_flag_bits {
> >  	__REQ_FS_PRIVATE,	/* for file system (submitter) use */
> >  	__REQ_ATOMIC,		/* for atomic write operations */
> >  	__REQ_P2PDMA,		/* contains P2P DMA pages */
> > +	__REQ_MMIO,		/* contains MMIO memory */
> >  	/*
> >  	 * Command specific flags, keep last:
> >  	 */
> > @@ -420,6 +421,7 @@ enum req_flag_bits {
> >  #define REQ_FS_PRIVATE	(__force blk_opf_t)(1ULL << __REQ_FS_PRIVATE)
> >  #define REQ_ATOMIC	(__force blk_opf_t)(1ULL << __REQ_ATOMIC)
> >  #define REQ_P2PDMA	(__force blk_opf_t)(1ULL << __REQ_P2PDMA)
> > +#define REQ_MMIO	(__force blk_opf_t)(1ULL << __REQ_MMIO)
> 
> Now that my integrity metadata DMA series is staged, I don't think we
> can use REQ flags like this because data and metadata may have different
> mapping types. I think we should add a flags field to the dma_iova_state
> instead.

Before integrity metadata code was merged, the assumption was that request is
only one type or p2p or host. Is it still holding now?

And we can't store in dma_iova_state() as HMM/RDMA code works in page-based
granularity and one dma_iova_state() can mix different types.

Thanks

>