linux-kernel - RE: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV

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Message-ID: <BN9PR11MB5276078BD0923AEEF15089AE8C892@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 6 May 2025 04:46:19 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, Jason Gunthorpe <jgg@...dia.com>
CC: Alexey Kardashevskiy <aik@....com>, "will@...nel.org" <will@...nel.org>,
	"joro@...tes.org" <joro@...tes.org>, "suravee.suthikulpanit@....com"
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	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>, "shuah@...nel.org"
	<shuah@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kselftest@...r.kernel.org"
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	<shameerali.kolothum.thodi@...wei.com>, "smostafa@...gle.com"
	<smostafa@...gle.com>, "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v2 06/19] iommufd/viommu: Add
 IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Tuesday, May 6, 2025 10:54 AM
> 
> On Mon, May 05, 2025 at 02:08:07PM -0300, Jason Gunthorpe wrote:
> > On Wed, Apr 30, 2025 at 12:58:47AM -0700, Nicolin Chen wrote:
> >
> > > > ... and I just hit a problem with it - this is basically guest BDFn
> > > > and it works as long as I'm hotplugging the TEE-IO VF into an SNP VM
> > > > but does not when I pass through via the QEMU cmdline - bus numbers
> > > > are not assigned yet. So I have to postpone the vdevice allocation
> > > > till run time, did I miss something here? Thanks,
> > >
> > > I have a similar case with QEMU ARM64's VM: so vDEVICE on ARM is
> > > allocated at runtime as well because the BDF number isn't ready
> > > at the boot time.
> >
> > Oh that's ugly then.. So you'll need to add some kind of 'modify
> > sid/bdf' operation I think.
> 
> But the initial vDEVICE would be still unusable. Its BDF number is
> literally 0 in my case. It can't be used for SID-based invalidation
> nor the reverse vSID lookup for fault injection..
> 

Agree that it makes more sense to allocate vDEVICE at runtime until
it's assigned with a valid bus number. and destroy/recreation is
required when the bus number is changed.