> From: Tian, Kevin <kevin.tian@xxxxxxxxx> > Sent: Tuesday, June 30, 2020 10:01 AM > > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > Sent: Monday, June 29, 2020 8:23 PM > > > > Hi Stefan, > > > > > From: Stefan Hajnoczi <stefanha@xxxxxxxxx> > > > Sent: Monday, June 29, 2020 5:25 PM > > > > > > On Wed, Jun 24, 2020 at 01:55:15AM -0700, Liu Yi L wrote: > > > > +/* > > > > + * struct iommu_nesting_info - Information for nesting-capable IOMMU. > > > > + * user space should check it before using > > > > + * nesting capability. > > > > + * > > > > + * @size: size of the whole structure > > > > + * @format: PASID table entry format, the same definition with > > > > + * @format of struct iommu_gpasid_bind_data. > > > > + * @features: supported nesting features. > > > > + * @flags: currently reserved for future extension. > > > > + * @data: vendor specific cap info. > > > > + * > > > > + * +---------------+----------------------------------------------------+ > > > > + * | feature | Notes | > > > > + * > > > > > +===============+=============================================== > > ==== > > > =+ > > > > + * | SYSWIDE_PASID | Kernel manages PASID in system wide, PASIDs > > used | > > > > + * | | in the system should be allocated by host kernel | > > > > + * +---------------+----------------------------------------------------+ > > > > + * | BIND_PGTBL | bind page tables to host PASID, the PASID could | > > > > + * | | either be a host PASID passed in bind request or | > > > > + * | | default PASIDs (e.g. default PASID of aux-domain) | > > > > + * +---------------+----------------------------------------------------+ > > > > + * | CACHE_INVLD | mandatory feature for nesting capable IOMMU > > | > > > > + * +---------------+----------------------------------------------------+ > > > > > > This feature description is vague about what CACHE_INVLD does and how > > to > > > use it. If I understand correctly, the presence of this feature means > > > that VFIO_IOMMU_NESTING_OP_CACHE_INVLD must be used? > > > > > > The same kind of clarification could be done for SYSWIDE_PASID and > > > BIND_PGTBL too. > > > > For SYSWIDE_PASID and BIND_PGTBL, yes, presence of the feature bit > > means must use. So the two are requirements to user space if it wants > > to setup nesting. While for CACHE_INVLD, it's kind of availability > > here. How about removing CACHE_INVLD as presence of BIND_PGTBL should > > indicates support of CACHE_INVLD? > > > > So far this assumption is correct but it may not be true when thinking forward. > For example, a vendor might find a way to allow the owner of 1st-level page > table to directly invalidate cache w/o going through host IOMMU driver. From > this angle I feel explicitly reporting this capability is more robust. I see. explicitly require 1st-level page table owner to do cache invalidation after modifying page table is fair to me. > Regarding to the description, what about below? > > -- > SYSWIDE_PASID: PASIDs are managed in system-wide, instead of per device. > When a device is assigned to userspace or VM, proper uAPI (provided by > userspace driver framework, e.g. VFIO) must be used to allocate/free PASIDs > for the assigned device. > > BIND_PGTBL: The owner of the first-level/stage-1 page table must explicitly > bind the page table to associated PASID (either the one specified in bind > request or the default PASID of the iommu domain), through VFIO_IOMMU > _NESTING_OP > > CACHE_INVLD: The owner of the first-level/stage-1 page table must > explicitly invalidate the IOMMU cache through VFIO_IOMMU_NESTING_OP, > according to vendor-specific requirement when changing the page table. > -- thanks for the statements, will apply. Regards, Yi Liu > Thanks > Kevin > >
