vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support

Previous work on dev-iotlb message broke vhost on either SMMU or virtio-iommu
since dev-iotlb (or PCIe ATS) is not yet supported for those archs.

An initial idea is that we can let IOMMU to export this information to vhost so
that vhost would know whether the vIOMMU would support dev-iotlb, then vhost
can conditionally register to dev-iotlb or the old iotlb way.  We can work
based on some previous patch to introduce PCIIOMMUOps as Yi Liu proposed [1].

However it's not as easy as I thought since vhost_iommu_region_add() does not
have a PCIDevice context at all since it's completely a backend.  It seems
non-trivial to pass over a PCI device to the backend during init.  E.g. when
the IOMMU notifier registered hdev->vdev is still NULL.

To make the fix smaller and easier, this patch goes the other way to leverage
the flag_changed() hook of vIOMMUs so that SMMU and virtio-iommu can trap the
dev-iotlb registration and fail it.  Then vhost could try the fallback solution
as using UNMAP invalidation for it's translations.

[1] https://lore.kernel.org/qemu-devel/[email protected]/

Reported-by: Eric Auger <[email protected]>
Fixes: b68ba1c
Reviewed-by: Eric Auger <[email protected]>
Tested-by: Eric Auger <[email protected]>
Signed-off-by: Peter Xu <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

Author: xzpeter

hw/arm/smmuv3.c

@@ -1497,6 +1497,11 @@ static int smmuv3_notify_flag_changed(IOMMUMemoryRegion *iommu,
     SMMUv3State *s3 = sdev->smmu;
     SMMUState *s = &(s3->smmu_state);
 
+    if (new & IOMMU_NOTIFIER_DEVIOTLB_UNMAP) {
+        error_setg(errp, "SMMUv3 does not support dev-iotlb yet");
+        return -EINVAL;
+    }
+
     if (new & IOMMU_NOTIFIER_MAP) {
         error_setg(errp,
                    "device %02x.%02x.%x requires iommu MAP notifier which is "

hw/virtio/vhost.c

@@ -704,6 +704,7 @@ static void vhost_iommu_region_add(MemoryListener *listener,
     Int128 end;
     int iommu_idx;
     IOMMUMemoryRegion *iommu_mr;
+    int ret;
 
     if (!memory_region_is_iommu(section->mr)) {
         return;
@@ -726,8 +727,16 @@ static void vhost_iommu_region_add(MemoryListener *listener,
     iommu->iommu_offset = section->offset_within_address_space -
                           section->offset_within_region;
     iommu->hdev = dev;
-    memory_region_register_iommu_notifier(section->mr, &iommu->n,
-                                          &error_fatal);
+    ret = memory_region_register_iommu_notifier(section->mr, &iommu->n, NULL);
+    if (ret) {
+        /*
+         * Some vIOMMUs do not support dev-iotlb yet.  If so, try to use the
+         * UNMAP legacy message
+         */
+        iommu->n.notifier_flags = IOMMU_NOTIFIER_UNMAP;
+        memory_region_register_iommu_notifier(section->mr, &iommu->n,
+                                              &error_fatal);
+    }
     QLIST_INSERT_HEAD(&dev->iommu_list, iommu, iommu_next);
     /* TODO: can replay help performance here? */
 }

hw/virtio/virtio-iommu.c

@@ -893,6 +893,11 @@ static int virtio_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu_mr,
                                             IOMMUNotifierFlag new,
                                             Error **errp)
 {
+    if (new & IOMMU_NOTIFIER_DEVIOTLB_UNMAP) {
+        error_setg(errp, "Virtio-iommu does not support dev-iotlb yet");
+        return -EINVAL;
+    }
+
     if (old == IOMMU_NOTIFIER_NONE) {
         trace_virtio_iommu_notify_flag_add(iommu_mr->parent_obj.name);
     } else if (new == IOMMU_NOTIFIER_NONE) {