> From: Nicolin Chen <nicolinc@xxxxxxxxxx> > Sent: Friday, May 24, 2024 11:26 AM > > On Fri, May 24, 2024 at 02:21:23AM +0000, Tian, Kevin wrote: > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > > 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@xxxxxxxxxx> > > > > > 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? > > Well, we haven't thought about a case of doing ATC invalidation > via VINTF/VCMDQ without setting up a VMID, as "VMID" is a field > in the VINTF_CONFIG register next to the Enable bit and must be > set prior to enabling a VINTF, though your understanding of the > HW work flow is probably accurate :) Okay, that explains it. they are irrelevant in concept but come relevant due to that detail. 😊 > > And the narrative at the top was trying to describe the links: > [ device ] => [ proxy identity S1 ] => [ viommu [ shared S2 ] ] > v.s. > [ device ] => [ non-shareable S2 ] > > So the first case can take advantage of VIOMMU_INVALIDATE v.s. > the second case requires a DEV_INVALIDATE. and one side-effect in the first case is to save one VMID for non-shareable S2 hence improves iotlb efficiency. > > Another conclusion between the lines: since ARM SMMU will have > the first case (with viommu), there is no longer any use of a > DEV_INVALIDATE ioctl. So, we would likely drop it in the coming > version. > > Thanks > Nicolin
