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

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Message-ID: <20250507122411.GA90261@nvidia.com>
Date: Wed, 7 May 2025 09:24:11 -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 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. At least some
arches will need something like that.

The "AMD IOMMU" I expected to be created by the viommu object.

Jason