linux-kernel - Re: [PATCH v2 2/2] block-dma: properly take MMIO path

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Message-ID: <3df0dd64-b2bc-4d3c-96b1-8ecc60d9de56@nvidia.com>
Date: Mon, 20 Oct 2025 23:37:38 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: Leon Romanovsky <leon@...nel.org>, Jens Axboe <axboe@...nel.dk>, Keith
 Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>, Sagi Grimberg
	<sagi@...mberg.me>
CC: "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] block-dma: properly take MMIO path

On 10/20/25 10:00, Leon Romanovsky wrote:
> From: Leon Romanovsky<leonro@...dia.com>
>
> 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.
>
> Link:https://lore.kernel.org/all/f912c446-1ae9-4390-9c11-00dce7bf0fd3@arm.com/
> Signed-off-by: Leon Romanovsky<leonro@...dia.com>

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

-ck