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

[Keith Busch <kbusch@kernel.org>]

On Thu, Aug 28, 2025 at 07:54:27PM +0300, Leon Romanovsky wrote:
> 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?

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.

> 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.

I see.