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

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Message-ID: <ZwAwWr+q3ZGkZCSM@Asurada-Nvidia>
Date: Fri, 4 Oct 2024 11:13:46 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...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 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?

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.

> The vdev_id is the iommu handle, and there is a platform specific
> transformation between Bus/Device/Function and the iommu handle. In
> some cases this is math, in some cases it is ACPI/DT tables or
> something.

> So I think the kernel should not make an assumption about the
> relationship.

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?

Thanks
Nicolin