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

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Message-ID: <20250509220717.GE5657@nvidia.com>
Date: Fri, 9 May 2025 19:07:17 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Alexey Kardashevskiy <aik@....com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	will@...nel.org, joro@...tes.org, suravee.suthikulpanit@....com,
	robin.murphy@....com, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
	shuah@...nel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
	yi.l.liu@...el.com
Subject: Re: [PATCH v2 06/19] iommufd/viommu: Add
 IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

On Fri, May 09, 2025 at 12:57:18PM +1000, Alexey Kardashevskiy wrote:
> 
> 
> On 7/5/25 22:24, Jason Gunthorpe wrote:
> > On Wed, May 07, 2025 at 09:18:29PM +1000, Alexey Kardashevskiy wrote:
> > 
> > > > We should not destroy the vdevice for something like that. In a CC
> > > > case that would unplug it from the VM which is not right.
> > > 
> > > vdevice is not directly seen by the guest, is not it? The guest will
> > > see, for example, an "AMD IOMMU" and assume there is device table
> > > for all 64K devices, and so on, it is QEMU which will be
> > > reallocating vdevice in the host's IOMMUFD. Did I miss something
> > > here? Thanks,
> > 
> > I imagined the vdevice would trigger the CC call to create the vPCI
> > function in the guest attached to the secure iommu.
> 
> What is this vPCI going to look like inside the guest? There still
> be AMD IOMMU PCI function and passed through to-be-trusted PCI
> function.

However the VMM tells it to look using the arguments to the create
vdevice ioctl?

I don't understand the question?

Jason