linux-kernel - Re: [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure for cleaner abstraction

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250729075209.GA23823@lst.de>
Date: Tue, 29 Jul 2025 09:52:09 +0200
From: Christoph Hellwig <hch@....de>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Christoph Hellwig <hch@....de>, Leon Romanovsky <leon@...nel.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>,
	Jérôme Glisse <jglisse@...hat.com>,
	Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, linux-pci@...r.kernel.org,
	Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure
 for cleaner abstraction

On Sun, Jul 27, 2025 at 03:51:58PM -0300, Jason Gunthorpe wrote:
> On Thu, Jul 24, 2025 at 09:59:22AM +0200, Christoph Hellwig wrote:
> > On Thu, Jul 24, 2025 at 10:55:33AM +0300, Leon Romanovsky wrote:
> > > Please, see last patch in the series https://lore.kernel.org/all/aea452cc27ca9e5169f7279d7b524190c39e7260.1753274085.git.leonro@nvidia.com
> > > It gives me a way to call p2p code with stable pointer for whole BAR.
> > > 
> > 
> > That simply can't work.
> 
> Why not?
> 
> That's the whole point of this, to remove struct page and use
> something else as a handle for the p2p when doing the DMA API stuff.

Because the struct page is the only thing that:

 a) dma-mapping works on
 b) is the only place we can discover the routing information, but also
    more importantly ensure that the underlying page is still present
    and the device is not hot unplugged, or in a very theoretical worst
    case replaced by something else.