From: Keith Busch <kbusch@kernel.org>
To: Leon Romanovsky <leon@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
Sagi Grimberg <sagi@grimberg.me>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nvme@lists.infradead.org
Subject: Re: [PATCH v4 2/2] block-dma: properly take MMIO path
Date: Wed, 12 Nov 2025 15:00:11 -0500 [thread overview]
Message-ID: <aRTnS1NZ0yEL0pJl@kbusch-mbp> (raw)
In-Reply-To: <20251112-block-with-mmio-v4-2-54aeb609d28d@nvidia.com>
On Wed, Nov 12, 2025 at 09:48:05PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.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.
>
> 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@kernel.org>
next prev parent reply other threads:[~2025-11-12 20:00 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-12 19:48 [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P DMA Leon Romanovsky
2025-11-12 19:48 ` [PATCH v4 1/2] nvme-pci: migrate to dma_map_phys instead of map_page Leon Romanovsky
2025-11-12 23:57 ` Chaitanya Kulkarni
2025-11-12 19:48 ` [PATCH v4 2/2] block-dma: properly take MMIO path Leon Romanovsky
2025-11-12 20:00 ` Keith Busch [this message]
2025-11-12 23:57 ` Chaitanya Kulkarni
2025-11-13 16:39 ` [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P DMA Jens Axboe
2025-11-13 17:12 ` Jens Axboe
2025-11-13 17:45 ` Jens Axboe
2025-11-13 19:50 ` Leon Romanovsky
2025-11-13 20:03 ` Keith Busch
2025-11-13 20:13 ` Leon Romanovsky
2025-11-13 20:40 ` Leon Romanovsky
2025-11-13 20:43 ` Jens Axboe
2025-11-14 8:13 ` Leon Romanovsky
2025-11-13 19:52 ` Keith Busch
2025-11-13 20:40 ` Jens Axboe
2025-11-14 8:16 ` Leon Romanovsky
2025-11-14 12:08 ` Jens Axboe
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