linux-kernel - Re: [PATCH v5 1/9] PCI/P2PDMA: Separate the mmap() support from the core logic

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: <20251022114333.GD21107@nvidia.com>
Date: Wed, 22 Oct 2025 08:43:33 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Leon Romanovsky <leon@...nel.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Leon Romanovsky <leonro@...dia.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>, 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 v5 1/9] PCI/P2PDMA: Separate the mmap() support from the
 core logic

On Wed, Oct 22, 2025 at 12:10:35AM -0700, Christoph Hellwig wrote:
> On Mon, Oct 20, 2025 at 09:58:54AM -0300, Jason Gunthorpe wrote:
> > I explained it in detail in the message you are repling to. If
> > something is not clear can you please be more specific??
> > 
> > Is it the mmap in VFIO perhaps that is causing these questions?
> > 
> > VFIO uses a PFNMAP VMA, so you can't pin_user_page() it. It uses
> > unmap_mapping_range() during its remove() path to get rid of the VMA
> > PTEs.
> 
> This all needs to g• into the explanation.
> 
> > Instead the DMABUF FD is used to pass the MMIO pages between VFIO and
> > another driver. DMABUF has a built in invalidation mechanism that VFIO
> > triggers before remove(). The invalidation removes access from the
> > other driver.
> > 
> > This is different than NVMe which has no invalidation. NVMe does
> > unmap_mapping_range() on the VMA and waits for all the short lived
> > pgmap references to clear. We don't need anything like that because
> > DMABUF invalidation is synchronous.
> 
> Please add documentation for this model to the source tree.

Okay, Lets see what we can come up with. I think explaining the dmabuf
model with respect to the p2p provider in the new common dmabuf
mapping API code would make sense.

Jason