Re: [PATCH v3 4/4] iommu/vt-d: Introduce batched cache invalidation

[Yi Liu]

On 2024/8/17 11:28, Baolu Lu wrote:
> On 2024/8/17 0:38, Jacob Pan wrote:
> > On Thu, 15 Aug 2024 14:52:21 +0800
> > Tina Zhang <tina.zhang@xxxxxxxxx> wrote:
> >
> > > @@ -270,7 +343,8 @@ static void cache_tag_flush_iotlb(struct
> > > dmar_domain *domain, struct cache_tag * u64 type = DMA_TLB_PSI_FLUSH;
> > >       if (domain->use_first_level) {
> > > -        qi_flush_piotlb(iommu, tag->domain_id, tag->pasid,
> > > addr, pages, ih);
> > > +        qi_batch_add_piotlb(iommu, tag->domain_id,
> > > tag->pasid, addr,
> > > +                    pages, ih, domain->qi_batch);
> > >           return;
> > >       }
> > > @@ -287,7 +361,8 @@ static void cache_tag_flush_iotlb(struct
> > > dmar_domain *domain, struct cache_tag * }
> > >       if (ecap_qis(iommu->ecap))
> > > -        qi_flush_iotlb(iommu, tag->domain_id, addr | ih,
> > > mask, type);
> > > +        qi_batch_add_iotlb(iommu, tag->domain_id, addr | ih,
> > > mask, type,
> > > +                   domain->qi_batch);
> > If I understand this correctly, IOTLB flush maybe deferred until the
> > batch array is full, right? If so, is there a security gap where
> > callers think the mapping is gone after the call returns?
> No. All related caches are flushed before function return. A domain can
> have multiple cache tags. Previously, we sent individual cache
> invalidation requests to hardware. This change combines all necessary
> invalidation requests into a single batch and raise them to hardware
> together to make it more efficient.

Hi Jacob,

Do you mean the configuration that iommu.strict==0? :) As the above
explanation from Baolu, this patch is not for that although it uses
the term "batched". Also, it would reduce the VMExits that due to the
IOTLB/DevTLB invalidation a lot in the virtualization environment.

--
Regards,
Yi Liu