linux-kernel - Re: [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev

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Date: Thu, 23 May 2024 10:33:58 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"joro@...tes.org" <joro@...tes.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-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	"eric.auger@...hat.com" <eric.auger@...hat.com>,
	"vasant.hegde@....com" <vasant.hegde@....com>,
	"jon.grimm@....com" <jon.grimm@....com>,
	"santosh.shukla@....com" <santosh.shukla@....com>,
	"Dhaval.Giani@....com" <Dhaval.Giani@....com>,
	"shameerali.kolothum.thodi@...wei.com" <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev_id ops

On Thu, May 23, 2024 at 05:44:40AM +0000, Tian, Kevin wrote:
> > On Sun, May 12, 2024 at 11:46:54AM -0300, Jason Gunthorpe wrote:
> > > On Fri, Apr 12, 2024 at 08:47:04PM -0700, Nicolin Chen wrote:
> > > > Add a pair of ops to set and unet device's virtual ID that belongs to
> > > > a viommu object. They will be used, in the following patch, by iommufd
> > > > to support some HW-acceleration feature from the host level.
> > > >
> > > > For instance, every device behind an ARM SMMU has a Stream ID. The ID
> > > > is used by ATC invalidation commands so SMMU HW can direct
> > invalidation
> > > > requests to the corresponding PCI device where the ID belongs to. In a
> > > > virtualization use case, a passthroughed device in the VM will have a
> > > > virtuail Stream ID, used by the ATC invalidation commands in the guest
> > > > system. NVIDIA's CMDQV extension for SMMUv3 provides a v-interface
> > to
> > > > execute the guest-level ATC invalidation commands directly, yet needs
> > > > the HW to be aware of its virtual Stream ID so it can replace with its
> > > > physical Stream ID.
> > >
> > > I imagine using this as well for the ATC invalidation commands. It
> > > would be very easy and simplifying if the command fixup just extracted
> > > the vSID from the ATC invalidation and used an xarray to turn it into
> > > a pSID and then pushed the resulting command.
> > 
> > You mean the nested SMMU series right? Actually the set_dev_id
> > ioctl was a part of that until we wanted to try DEV_INVALIDATE.
> > 
> > So again, yes, it makes sense to me that we move viommu and the
> > set_dev_id to the nested series, and then drop DEV_INVALIDATE.
> > 
> 
> I'm right about to ask how the nesting series is going. Per earlier
> discussion iirc the nesting series will go in before VCMDQ?

It has been sitting on my github, since it is now the N+1 series to
merge I will post it in a few weeks. There are still some details
yet to be typed in unfortunately.

Jason