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

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Date: Thu, 23 May 2024 05:44:40 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, Jason Gunthorpe <jgg@...dia.com>
CC: "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

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Monday, May 13, 2024 12:39 PM
> 
> 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?