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

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Message-ID: <20241004185019.GJ1365916@nvidia.com>
Date: Fri, 4 Oct 2024 15:50:19 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Alexey Kardashevskiy <aik@....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, Oct 04, 2024 at 11:13:46AM -0700, Nicolin Chen wrote:
> On Fri, Oct 04, 2024 at 08:41:47AM -0300, Jason Gunthorpe wrote:
> > On Fri, Oct 04, 2024 at 02:32:28PM +1000, Alexey Kardashevskiy wrote:
> > > For my SEV-TIO exercise ("trusted IO"), I am looking for a kernel interface
> > > to pass the guest's BDFs for a specific host device (which is passed
> > > through) and nothing in the kernel has any knowledge of it atm, is this the
> > > right place, or another ioctl() is needed here?
> > 
> > We probably need to add the vRID as well to this struct for that
> > reason.
> 
> "vRID"/"vBDF" doesn't sound very generic to me to put in this
> structure, though PCI devices are and very likely will be the
> only users of this Virtual Device for a while. Any good idea?

It isn't necessarily bad to have a pci field as long as we can
somehow understand when it is used.

> Also, I am wondering if the uAPI structure of Virtual Device
> should have a driver-specific data structure. And the vdev_id
> should be in the driver-specific struct. So, it could stay in
> corresponding naming, "Stream ID", "Device ID" or "Context ID"
> v.s. a generic "Virtual ID" in the top-level structure? Then,
> other info like CCA can be put in the driver-level structure
> of SMMU's.

I'd to avoid a iommu-driver specific structure here, but I fear we
will have a "lowervisor" (sigh) specific structure for the widely
varied CC/pkvm/etc world.

> Agreed. That also implies that a vRID is quite independent to
> the IOMMU right? So, I think that the reason of adding a vRID
> to the virtual deivce uAPI/structure should be IOMMU requiring
> it?

I would like to use this API to link in the CC/pkvm/etc world, and use
it to create not just the vIOMMU components but link up to the
"lowervisor" components as well, since it is all the same stuff
basically.

Jason