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

[Liu, Yi L]

> From: Liu, Yi L
> Sent: Wednesday, March 25, 2020 9:22 PM
> To: 'Peter Xu' <address@hidden>
> Subject: RE: [PATCH v1 20/22] intel_iommu: propagate PASID-based iotlb
> invalidation to host
> 
> > From: Peter Xu <address@hidden>
> > Sent: Wednesday, March 25, 2020 2:34 AM
> > To: Liu, Yi L <address@hidden>
> > Subject: Re: [PATCH v1 20/22] intel_iommu: propagate PASID-based iotlb
> > invalidation to host
> >
> > On Sun, Mar 22, 2020 at 05:36:17AM -0700, Liu Yi L wrote:
> > > This patch propagates PASID-based iotlb invalidation to host.
> > >
> > > Intel VT-d 3.0 supports nested translation in PASID granular.
> > > Guest SVA support could be implemented by configuring nested
> > > translation on specific PASID. This is also known as dual stage DMA
> > > translation.
> > >
> > > Under such configuration, guest owns the GVA->GPA translation which
> > > is configured as first level page table in host side for a specific
> > > pasid, and host owns GPA->HPA translation. As guest owns first level
> > > translation table, piotlb invalidation should be propagated to host
> > > since host IOMMU will cache first level page table related mappings
> > > during DMA address translation.
> > >
> > > This patch traps the guest PASID-based iotlb flush and propagate it
> > > to host.
> > >
> > > Cc: Kevin Tian <address@hidden>
> > > Cc: Jacob Pan <address@hidden>
> > > Cc: Peter Xu <address@hidden>
> > > Cc: Yi Sun <address@hidden>
> > > Cc: Paolo Bonzini <address@hidden>
> > > Cc: Richard Henderson <address@hidden>
> > > Cc: Eduardo Habkost <address@hidden>
> > > Signed-off-by: Liu Yi L <address@hidden>
> > > ---
> > >  hw/i386/intel_iommu.c          | 139
> > +++++++++++++++++++++++++++++++++++++++++
> > >  hw/i386/intel_iommu_internal.h |   7 +++
> > >  2 files changed, 146 insertions(+)
> > >
> > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c index
> > > b9ac07d..10d314d 100644
> > > --- a/hw/i386/intel_iommu.c
> > > +++ b/hw/i386/intel_iommu.c
> > > @@ -3134,15 +3134,154 @@ static bool
> > vtd_process_pasid_desc(IntelIOMMUState *s,
> > >      return (ret == 0) ? true : false;  }
> > >
> > > +/**
> > > + * Caller of this function should hold iommu_lock.
> > > + */
> > > +static void vtd_invalidate_piotlb(IntelIOMMUState *s,
> > > +                                  VTDBus *vtd_bus,
> > > +                                  int devfn,
> > > +                                  DualIOMMUStage1Cache
> > > +*stage1_cache) {
> > > +    VTDHostIOMMUContext *vtd_dev_icx;
> > > +    HostIOMMUContext *host_icx;
> > > +
> > > +    vtd_dev_icx = vtd_bus->dev_icx[devfn];
> > > +    if (!vtd_dev_icx) {
> > > +        goto out;
> > > +    }
> > > +    host_icx = vtd_dev_icx->host_icx;
> > > +    if (!host_icx) {
> > > +        goto out;
> > > +    }
> > > +    if (host_iommu_ctx_flush_stage1_cache(host_icx, stage1_cache)) {
> > > +        error_report("Cache flush failed");
> >
> > I think this should not easily be triggered by the guest, but just in
> > case... Let's use
> > error_report_once() to be safe.
> 
> Agreed.
> 
> > > +    }
> > > +out:
> > > +    return;
> > > +}
> > > +
> > > +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.

Regards,
Yi Liu