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

On Thu, Aug 28, 2025 at 01:10:32PM -0600, Keith Busch wrote:

On Thu, Aug 28, 2025 at 03:41:15PM -0300, Jason Gunthorpe wrote:

quoted

On Thu, Aug 28, 2025 at 11:15:20AM -0600, Keith Busch wrote:

quoted

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.

In that case the new bit leon proposes should only be used for the
unmap of the data pages and the metadata unmap should always be
unmapped as CPU?

Jason