Messages in this thread | | | Date | Thu, 23 Mar 2023 09:16:51 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v1 14/14] iommu/arm-smmu-v3: Add arm_smmu_cache_invalidate_user |
| |
On Wed, Mar 22, 2023 at 01:43:59PM -0700, Nicolin Chen wrote:
> > So I think for ARM we want to reflect the physical SMMU instances into > > vSMMU instances and that feels best done by having a unique S2 > > iommu_domain for each SMMU instance. Then we know that an invalidation > > for a SMMU instance is delivered to that S2's singular CMDQ and things > > like vCMDQ become possible. > > In that environment, do we still need a VMID unification?
If each S2 is per-smmu-instance then the VMID can be local to the SMMU instance
> > > Our approach of setting up a stage-2 mapping in QEMU is to > > > map the entire guest memory. I don't see a point in having > > > a separate S2 domain, even if there are multiple instances? > > > > And then this is the drawback, we don't really want to have duplicated > > S2 page tables in the system for every stage 2. > > > > Maybe we have made a mistake by allowing the S2 to be an unmanaged > > domain. Perhaps we should create the S2 out of an unmanaged domain > > like the S1. > > > > Then the rules could be > > - Unmanaged domain can be used with every smmu instance, only one > > copy of the page table. The ASID in the iommu_domain is > > kernel-global > > - S2 domain is a child of a shared unmanaged domain. It can be used > > only with the SMMU it is associated with, it has a per-SMMU VM ID > > - S1 domain is a child of a S2 domain, it can be used only with the > > SMMU it's S2 is associated with, just because > > The actual S2 pagetable has to stay at the unmanaged domain > for IOAS_MAP, while we maintain an s2_cfg data structure in > the shadow S2 domain per SMMU instance that has its own VMID > but a shared S2 page table pointer?
Yes
> Hmm... Feels very complicated to me. How does that help?
It de-duplicates the page table across multiple SMMU instances.
> > So, I have been exploring a different approach by creating an > > > internal multiplication inside VCMDQ... > > > > How can that work? > > > > You'd have to have the guest VM to know to replicate to different > > vCMDQ's? Which isn't the standard SMMU programming model anymore.. > > VCMDQ has multiple VINTFs (Virtual Interfaces) that's supposed > to be used by the host to expose to multiple VMs. > > In a multi-SMMU environment, every single SMMU+VCMDQ instance > would have one VINTF only that contains one or more VCMDQs. In > this case, passthrough devices behind different physical SMMU > instances are straightforwardly attached to different vSMMUs.
Yes, this is the obvious simple impementation
> However, if we can't have multiple vSMMU instances, the guest > VM (its HW) would enable multiple VINTFs corresponding to the > number of physical SMMU/VCMDQ instances, for devices to attach > accordingly. That means I need to figure out a way to pin the > devices onto those VINTFs, by somehow passing their physical > SMMU IDs.
And a way to request the correctly bound vCMDQ from the guest as well. Sounds really messsy, I'd think multi-smmu is the much cleaner choice
Jason
| |