linux-kernel - Re: [PATCH v1 00/17] Provide a new two step DMA mapping API

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Message-ID: <20241108150500.GA10102@lst.de>
Date: Fri, 8 Nov 2024 16:05:00 +0100
From: Christoph Hellwig <hch@....de>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
	Leon Romanovsky <leon@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Sagi Grimberg <sagi@...mberg.me>, Keith Busch <kbusch@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org, matthew.brost@...el.com,
	Thomas.Hellstrom@...ux.intel.com, brian.welty@...el.com,
	himal.prasad.ghimiray@...el.com, krishnaiah.bommu@...el.com,
	niranjana.vishwanathapura@...el.com
Subject: Re: [PATCH v1 00/17] Provide a new two step DMA mapping API

On Fri, Nov 08, 2024 at 11:02:26AM -0400, Jason Gunthorpe wrote:
> It is fully OK? Can't dma_map_page() trigger swiotlb? It must not do
> that for P2P. How does it know the difference if it just gets a phys?

dma_direct_map_page checks for p2p pages in the swiotlb bounce
path already in the current kernel, and dma_map_sg relies on exactly
that check to prevent bouncing for p2p.