Re: [PATCH v4 2/2] block-dma: properly take MMIO path

[Keith Busch]

On Wed, Nov 12, 2025 at 09:48:05PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@xxxxxxxxxx>
> 
> In commit eadaa8b255f3 ("dma-mapping: introduce new DMA attribute to
> indicate MMIO memory"), DMA_ATTR_MMIO attribute was added to describe
> MMIO addresses, which require to avoid any memory cache flushing, as
> an outcome of the discussion pointed in Link tag below.
> 
> In case of PCI_P2PDMA_MAP_THRU_HOST_BRIDGE transfer, blk-mq-dm logic
> treated this as regular page and relied on "struct page" DMA flow.
> That flow performs CPU cache flushing, which shouldn't be done here,
> and doesn't set IOMMU_MMIO flag in DMA-IOMMU case.
> 
> As a solution, let's encode peer-to-peer transaction type in NVMe IOD
> flags variable and provide it to blk-mq-dma API.

Looks good.

Reviewed-by: Keith Busch <kbusch@xxxxxxxxxx>