Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

Jean-Philippe Brucker
2021-05-06T07:24:13Z

On Wed, May 05, 2021 at 01:04:46PM -0700, Jacob Pan wrote:
> > > For ARM, since the guest owns the per device PASID table. There is no
> > > need to allocate PASIDs from the host nor the hypervisor. Without SWQ,
> > > there is no need for global PASID/SSID either. So PASID being global
> > > for ARM is for simplicity in case of host PASID/SSID.
> >
> > It isn't clear how ARM can support PASID and mdev but that is an
> > unrelated issue..
> >
> AFAIK, the current SMMU device assignment is per RID, since only one stage2
> page tables per RID, not per PASID. This is equivalent to the older VT-d
> spec. prior to scalable mode.

Yes that's right. Since SMMUv3 has a single level-2 page table per RID, it
doesn't support assigning level-1 page tables to guests for mdevs (sub-VF
devices). So no PASIDs for mdevs, which also means each guest has its own
PASID space and the host doesn't track guest PASIDs.

Thanks,
Jean