RE: [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev_id ops

Tian, Kevin
2024-05-24T02:21:30Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, May 23, 2024 11:01 PM
>
> On Thu, May 23, 2024 at 06:19:59AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Wednesday, May 22, 2024 2:25 AM
> > >
> > > On Tue, May 14, 2024 at 06:59:07PM -0700, Nicolin Chen wrote:
> > > > So, you want a proxy S1 domain for a device to attach, in case
> > > > of a stage-2 only setup, because an S2 domain will no longer has
> > > > a VMID, since it's shared among viommus. In the SMMU driver case,
> > > > an arm_smmu_domain won't have an smmu pointer, so a device can't
> > > > attach to an S2 domain but always an nested S1 domain, right?
> > >
> > > That seems like a simple solution to the VMID lifetime, but it means
> > > the kernel has to decode more types of vSTE.
> > >
> >
> > why does ATC invalidation need to know about VMID?
>
> ATC invalidation always requires a vRID to pRID translation and the
> VIOMMU will hold that translation.
>
> On vCMDQ HW and on AMD HW the vRID to pRID translation is pushed into
> HW, and vCMDQ requires the VMID to do that.
>

At a quick glance VMID and vRID->pRID translation are both configurations
of a vintf.

My impression was that vintf->vmid is added to guest cmd when it's
about iotlb invalidation.

then vintf->sid_slots is walked when handling a guest cmd for ATC
invalidation.

I'm not sure why the latter one requires a valid VMID to do the walking
except it's a implementation choice made by vCMDQ?