Re: [PATCH 3/3] intel-iommu: build iova tree during IOMMU translation

[Peter Xu]

On Tue, Nov 29, 2022 at 04:10:37PM +0800, Jason Wang wrote:
> The IOVA tree is only built during page walk this breaks the device
> that tries to use UNMAP notifier only. One example is vhost-net, it
> tries to use UNMAP notifier when vIOMMU doesn't support DEVIOTLB_UNMAP
> notifier (e.g when dt mode is not enabled). The interesting part is
> that it doesn't use MAP since it can query the IOMMU translation by
> itself upon a IOTLB miss.
> 
> This doesn't work since Qemu doesn't build IOVA tree in IOMMU
> translation which means the UNMAP notifier won't be triggered during
> the page walk since Qemu think it is never mapped. This could be
> noticed when vIOMMU is used with vhost_net but dt is disabled.
> 
> Fixing this by build the iova tree during IOMMU translation, this
> makes sure the UNMAP notifier event could be identified during page
> walk. And we need to walk page table not only for UNMAP notifier but
> for MAP notifier during PSI.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/i386/intel_iommu.c | 43 ++++++++++++++++++-------------------------
>  1 file changed, 18 insertions(+), 25 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index d025ef2873..edeb62f4b2 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -1834,6 +1834,8 @@ static bool vtd_do_iommu_translate(VTDAddressSpace 
> *vtd_as, PCIBus *bus,
>      uint8_t access_flags;
>      bool rid2pasid = (pasid == PCI_NO_PASID) && s->root_scalable;
>      VTDIOTLBEntry *iotlb_entry;
> +    const DMAMap *mapped;
> +    DMAMap target;
>  
>      /*
>       * We have standalone memory region for interrupt addresses, we
> @@ -1954,6 +1956,21 @@ out:
>      entry->translated_addr = vtd_get_slpte_addr(slpte, s->aw_bits) & 
> page_mask;
>      entry->addr_mask = ~page_mask;
>      entry->perm = access_flags;
> +
> +    target.iova = entry->iova;
> +    target.size = entry->addr_mask;
> +    target.translated_addr = entry->translated_addr;
> +    target.perm = entry->perm;
> +
> +    mapped = iova_tree_find(vtd_as->iova_tree, &target);
> +    if (!mapped) {
> +        /* To make UNMAP notifier work, we need build iova tree here
> +         * in order to have the UNMAP iommu notifier to be triggered
> +         * during the page walk.
> +         */
> +        iova_tree_insert(vtd_as->iova_tree, &target);
> +    }
> +
>      return true;
>  
>  error:
> @@ -2161,31 +2178,7 @@ static void 
> vtd_iotlb_page_invalidate_notify(IntelIOMMUState *s,
>          ret = vtd_dev_to_context_entry(s, pci_bus_num(vtd_as->bus),
>                                         vtd_as->devfn, &ce);
>          if (!ret && domain_id == vtd_get_domain_id(s, &ce, vtd_as->pasid)) {
> -            if (vtd_as_has_map_notifier(vtd_as)) {
> -                /*
> -                 * As long as we have MAP notifications registered in
> -                 * any of our IOMMU notifiers, we need to sync the
> -                 * shadow page table.
> -                 */
> -                vtd_sync_shadow_page_table_range(vtd_as, &ce, addr, size);
> -            } else {
> -                /*
> -                 * For UNMAP-only notifiers, we don't need to walk the
> -                 * page tables.  We just deliver the PSI down to
> -                 * invalidate caches.
> -                 */
> -                IOMMUTLBEvent event = {
> -                    .type = IOMMU_NOTIFIER_UNMAP,
> -                    .entry = {
> -                        .target_as = &address_space_memory,
> -                        .iova = addr,
> -                        .translated_addr = 0,
> -                        .addr_mask = size - 1,
> -                        .perm = IOMMU_NONE,
> -                    },
> -                };
> -                memory_region_notify_iommu(&vtd_as->iommu, 0, event);

Isn't this path the one that will be responsible for pass-through the UNMAP
events from guest to vhost when there's no MAP notifier requested?

At least that's what I expected when introducing the iova tree, because for
unmap-only device hierachy I thought we didn't need the tree at all.

Jason, do you know where I miss?

Thanks,

> -            }
> +            vtd_sync_shadow_page_table_range(vtd_as, &ce, addr, size);
>          }
>      }
>  }
> -- 
> 2.25.1
> 

-- 
Peter Xu