RE: [PATCH v1 20/22] intel_iommu: propagate PASID-based iotlb invalidation to host

[Liu, Yi L]

> From: Peter Xu <address@hidden>
> Sent: Thursday, March 26, 2020 9:23 PM
> To: Liu, Yi L <address@hidden>
> Subject: Re: [PATCH v1 20/22] intel_iommu: propagate PASID-based iotlb
> invalidation to host
> 
> On Thu, Mar 26, 2020 at 09:02:48AM -0400, Peter Xu wrote:
> 
> [...]
> 
> > > > > > +static inline bool vtd_pasid_cache_valid(
> > > > > > +                          VTDPASIDAddressSpace *vtd_pasid_as) {
> > > > > > +    return vtd_pasid_as->iommu_state &&
> >                     ^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > > > >
> > > > > This check can be dropped because always true?
> > > > >
> > > > > If you agree with both the changes, please add:
> > > > >
> > > > > Reviewed-by: Peter Xu <address@hidden>
> > > >
> > > > I think the code should ensure all the pasid_as in hash table is
> > > > valid. And we can since all the operations are under protection of 
> > > > iommu_lock.
> > > >
> > > Peter,
> > >
> > > I think my reply was wrong. pasid_as in has table may be stale since
> > > the per pasid_as cache_gen may be not identical with the cache_gen
> > > in iommu_state. e.g. vtd_pasid_cache_reset() only increases the
> > > cache_gen in iommu_state. So there will be pasid_as in hash table
> > > which has cached pasid entry but its cache_gen is not equal to the
> > > one in iommu_state. For such pasid_as, we should treat it as stale.
> > > So I guess the vtd_pasid_cache_valid() is still necessary.
> >
> > I guess you misread my comment. :)
> >
> > I was saying the "vtd_pasid_as->iommu_state" check is not needed,
> > because iommu_state was always set if the address space is created.
> > vtd_pasid_cache_valid() is needed.
> >
> > Also, please double confirm that vtd_pasid_cache_reset() should drop
> > all the address spaces (as I think it should), not "only increase the
> > cache_gen".  IMHO you should only increase the cache_gen in the PSI
> > hook (vtd_pasid_cache_psi()) only.
> 
> Sorry, I mean GSI (vtd_pasid_cache_gsi), not PSI.

Got it.. Really confused me. :-) 

Regards,
Yi Liu