Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context change

[Baolu Lu]

On 7/2/24 9:47 AM, Baolu Lu wrote:
> On 7/2/24 9:11 AM, Tian, Kevin wrote:
> > > From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > > Sent: Monday, July 1, 2024 7:23 PM
> > > +
> > > +    /*
> > > +     * For scalable mode:
> > > +     * - Domain-selective PASID-cache invalidation to affected domains
> > > +     * - Domain-selective IOTLB invalidation to affected domains
> > > +     * - Global Device-TLB invalidation to affected functions
> > > +     */
> > > +    if (flush_domains) {
> > > +        /*
> > > +         * If the IOMMU is running in scalable mode and there might
> > > +         * be potential PASID translations, the caller should hold
> > > +         * the lock to ensure that context changes and cache flushes
> > > +         * are atomic.
> > > +         */
> > > +        assert_spin_locked(&iommu->lock);
> > > +        for (i = 0; i < info->pasid_table->max_pasid; i++) {
> > > +            pte = intel_pasid_get_entry(info->dev, i);
> > > +            if (!pte || !pasid_pte_is_present(pte))
> > > +                continue;
> > > +
> > > +            did = pasid_get_domain_id(pte);
> > > +            qi_flush_pasid_cache(iommu, did,
> > > QI_PC_ALL_PASIDS, 0);
> > > +            iommu->flush.flush_iotlb(iommu, did, 0, 0,
> > > DMA_TLB_DSI_FLUSH);
> > > +        }
> > > +    }
> > > +
> > > +    __context_flush_dev_iotlb(info);
> > > +}
> > this only invalidates devtlb w/o PASID. We miss a pasid devtlb 
> > invalidation
> > with global bit set.
>
> I am not sure about this. The spec says "Global Device-TLB invalidation
> to affected functions", I am not sure whether this implies any PASID-
> based-Device-TLB invalidation.

I just revisited the spec, Device-TLB invalidation only covers caches
for requests-without-PASID. If pasid translation is affected while
updating the context entry, we should also take care of the caches for
requests-with-pasid.

I will add below line to address this.

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index 9a7b5668c723..91db0876682e 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -932,6 +932,7 @@ void intel_context_flush_present(struct 
device_domain_info *info,
                        did = pasid_get_domain_id(pte);
                        qi_flush_pasid_cache(iommu, did, 
QI_PC_ALL_PASIDS, 0);
                        iommu->flush.flush_iotlb(iommu, did, 0, 0, 
DMA_TLB_DSI_FLUSH);
+                       pasid_cache_invalidation_with_pasid(iommu, did, i);
                }
        }

Thanks!

Best regards,
baolu