linux-kernel - Re: [TECH TOPIC] vfio, iommufd: Enabling user space drivers to vend more granular access to client processes

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Message-ID: <20250922175120.GA2547959@ziepe.ca>
Date: Mon, 22 Sep 2025 14:51:20 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alex Mastro <amastro@...com>
Cc: Mostafa Saleh <smostafa@...gle.com>,
	"Tian, Kevin" <kevin.tian@...el.com>,
	Keith Busch <kbusch@...nel.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, David Reiss <dreiss@...a.com>,
	Joerg Roedel <joro@...tes.org>, Leon Romanovsky <leon@...nel.org>,
	Li Zhe <lizhe.67@...edance.com>, Mahmoud Adam <mngyadam@...zon.de>,
	Philipp Stanner <pstanner@...hat.com>,
	Robin Murphy <robin.murphy@....com>,
	"Kasireddy, Vivek" <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>, Yunxiang Li <Yunxiang.Li@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [TECH TOPIC] vfio, iommufd: Enabling user space drivers to vend
 more granular access to client processes

On Mon, Sep 22, 2025 at 10:46:23AM -0700, Alex Mastro wrote:

> Following a dma_buf_ops.mmap, I suppose that revocation would mean:

I'd investigate adding some ioctl to the dmabuf fd to permanently
revoke it. The zapping/etc already has to be done just to get mmap in
the first place. The vending process would retain a FD on the dmabuf
and when it is time to revoke it then it can call the ioctl directly
on the fd to revoke.

Jason