linux-kernel - Re: [PATCH RFCv2 09/13] iommufd: Add IOMMU_OPTION_SW_MSI

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Message-ID: <20250129201556.GK5556@nvidia.com>
Date: Wed, 29 Jan 2025 16:15:56 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Eric Auger <eric.auger@...hat.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, will@...nel.org,
	robin.murphy@....com, kevin.tian@...el.com, tglx@...utronix.de,
	maz@...nel.org, alex.williamson@...hat.com, joro@...tes.org,
	shuah@...nel.org, reinette.chatre@...el.com, yebin10@...wei.com,
	apatel@...tanamicro.com, shivamurthy.shastri@...utronix.de,
	bhelgaas@...gle.com, anna-maria@...utronix.de, yury.norov@...il.com,
	nipun.gupta@....com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
	patches@...ts.linux.dev, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com
Subject: Re: [PATCH RFCv2 09/13] iommufd: Add IOMMU_OPTION_SW_MSI_START/SIZE
 ioctls

On Wed, Jan 29, 2025 at 06:49:22PM +0100, Eric Auger wrote:
> > If it was overriden inside iommufd then the user told the kernel what
> > range to use to override it. I don't need to go back and report back
> > to userspace information that it already gave to the kernel..
> 
> Looks strange to me because info exposed in sysfs is wrong then. What if
> someone else relies on this info, either at kernel level through the
> get_resv_regions callback or from user space.

Nothing else should call get_resv_regions() because VFIO is bound to
the device and iommufd owns the domain. We expect some exclusivity
here :)

sysfs for sw_msi should be understood as reporting the driver
recommendation, not anything to do with the current MSI operation of
the device.

Jason