linux-kernel - Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar mapping with IORESOURCE

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Message-ID: <20250805161035.GW26511@ziepe.ca>
Date: Tue, 5 Aug 2025 13:10:35 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	linux-coco@...ts.linux.dev, kvmarm@...ts.linux.dev,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	aik@....com, lukas@...ner.de, Samuel Ortiz <sameo@...osinc.com>,
	Suzuki K Poulose <Suzuki.Poulose@....com>,
	Steven Price <steven.price@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar
 mapping with IORESOURCE_EXCLUSIVE

On Tue, Aug 05, 2025 at 10:26:06AM +0800, Xu Yilun wrote:
> > IMHO there is no use case for that, it should arguably be global to
> > the whole kernel.
> 
> I think there are 2 topics here:
> 
> 1. Prevent VFIO mmap
> 2. Prevent /sys/../resource, /dev/mem users
> 
> I assume you are refering to the 2nd, then I agree.

Yes, the region stuff is only about #2.

> > 
> > > The original purpose of this pci_region_request_*() is to prevent
> > > further mmap/read/write against a vfio_cdev FD which would be used
> > 
> > No way, the VFIO internal mmap should be controled by VFIO not by
> 
> I assume your point is never to use more than one request region in the
> same driver to achieve some mutual exclusion. I'm good to it. We could
> switch to some bound flag.

Yes and yes

> > The only thing request region should do is prevent /sys/../resource,
> > /dev/mem users and so on, which is why it can and should be
> > global. Arguably VFIO should always block those things but
> > historically hasn't..
> 
> Agree. So seems no need a global option?

I'd ask Alex if he is OK with a global behavior change to make vfio
exclusive, after any required fixing to make vfio only request the
regions once at driver probe time..

Jason