[PATCH v2] vhost: Warn if DEVIOTLB_UNMAP is not supported and ats is set

[Eric Auger]

Since b68ba1ca5767 ("memory: Add IOMMU_NOTIFIER_DEVIOTLB_UNMAP
IOMMUTLBNotificationType"), vhost attempts to register DEVIOTLB_UNMAP
notifier. This latter is supported by the intel-iommu which supports
device-iotlb if the corresponding option is set. Then 958ec334bca3
("vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support") allowed
silent fallback to the legacy UNMAP notifier if the viommu does not
support device iotlb.

Initially vhost/viommu integration was introduced with intel iommu
assuming ats=on was set on virtio-pci device and device-iotlb was set
on the intel iommu. vhost acts as an ATS capable device since it
implements an IOTLB on kernel side. However translated transactions
that hit the device IOTLB do not transit through the vIOMMU. So this
requires a limited ATS support on viommu side. Anyway this assumed
ATS was eventually enabled .

But neither SMMUv3 nor virtio-iommu do support ATS and the integration
with vhost just relies on the fact those vIOMMU send UNMAP notifications
whenever the guest trigger them. This works without ATS being enabled.

This patch makes sure we get a warning if ATS is set on a device
protected by virtio-iommu or vsmmuv3, reminding that we don't have
full support of ATS on those vIOMMUs and setting ats=on on the
virtio-pci end-point is not a requirement.

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---

v1 -> v2:
- s/enabled/capable
- tweak the error message on vhost side
---
 include/hw/virtio/virtio-bus.h |  3 +++
 hw/virtio/vhost.c              | 21 ++++++++++++++++++++-
 hw/virtio/virtio-bus.c         | 14 ++++++++++++++
 hw/virtio/virtio-pci.c         | 11 +++++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index 7ab8c9dab0..23360a1daa 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -94,6 +94,7 @@ struct VirtioBusClass {
     bool has_variable_vring_alignment;
     AddressSpace *(*get_dma_as)(DeviceState *d);
     bool (*iommu_enabled)(DeviceState *d);
+    bool (*ats_capable)(DeviceState *d);
 };
 
 struct VirtioBusState {
@@ -157,4 +158,6 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int 
n, bool assign);
 void virtio_bus_cleanup_host_notifier(VirtioBusState *bus, int n);
 /* Whether the IOMMU is enabled for this device */
 bool virtio_bus_device_iommu_enabled(VirtIODevice *vdev);
+/* Whether ATS is enabled for this device */
+bool virtio_bus_device_ats_capable(VirtIODevice *vdev);
 #endif /* VIRTIO_BUS_H */
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 5185c15295..3cf9efce5e 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -324,6 +324,16 @@ static bool vhost_dev_has_iommu(struct vhost_dev *dev)
     }
 }
 
+static bool vhost_dev_ats_capable(struct vhost_dev *dev)
+{
+    VirtIODevice *vdev = dev->vdev;
+
+    if (vdev && virtio_bus_device_ats_capable(vdev)) {
+        return true;
+    }
+    return false;
+}
+
 static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
                               hwaddr *plen, bool is_write)
 {
@@ -737,6 +747,7 @@ static void vhost_iommu_region_add(MemoryListener *listener,
     Int128 end;
     int iommu_idx;
     IOMMUMemoryRegion *iommu_mr;
+    Error *err = NULL;
     int ret;
 
     if (!memory_region_is_iommu(section->mr)) {
@@ -760,8 +771,16 @@ static void vhost_iommu_region_add(MemoryListener 
*listener,
     iommu->iommu_offset = section->offset_within_address_space -
                           section->offset_within_region;
     iommu->hdev = dev;
-    ret = memory_region_register_iommu_notifier(section->mr, &iommu->n, NULL);
+    ret = memory_region_register_iommu_notifier(section->mr, &iommu->n, &err);
     if (ret) {
+        if (vhost_dev_ats_capable(dev)) {
+            error_reportf_err(err,
+                              "%s: Although the device exposes ATS capability, 
"
+                              "fallback to legacy IOMMU UNMAP notifier: ",
+                              iommu_mr->parent_obj.name);
+        } else {
+            error_free(err);
+        }
         /*
          * Some vIOMMUs do not support dev-iotlb yet.  If so, try to use the
          * UNMAP legacy message
diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 896feb37a1..d46c3f8ec4 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -348,6 +348,20 @@ bool virtio_bus_device_iommu_enabled(VirtIODevice *vdev)
     return klass->iommu_enabled(qbus->parent);
 }
 
+bool virtio_bus_device_ats_capable(VirtIODevice *vdev)
+{
+    DeviceState *qdev = DEVICE(vdev);
+    BusState *qbus = BUS(qdev_get_parent_bus(qdev));
+    VirtioBusState *bus = VIRTIO_BUS(qbus);
+    VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);
+
+    if (!klass->ats_capable) {
+        return false;
+    }
+
+    return klass->ats_capable(qbus->parent);
+}
+
 static void virtio_bus_class_init(ObjectClass *klass, void *data)
 {
     BusClass *bus_class = BUS_CLASS(klass);
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index e7d80242b7..c2ceba98a6 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1141,6 +1141,16 @@ static bool virtio_pci_iommu_enabled(DeviceState *d)
     return true;
 }
 
+static bool virtio_pci_ats_capable(DeviceState *d)
+{
+    VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
+
+    if (proxy->flags & VIRTIO_PCI_FLAG_ATS) {
+        return true;
+    }
+    return false;
+}
+
 static bool virtio_pci_queue_enabled(DeviceState *d, int n)
 {
     VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
@@ -2229,6 +2239,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, 
void *data)
     k->ioeventfd_assign = virtio_pci_ioeventfd_assign;
     k->get_dma_as = virtio_pci_get_dma_as;
     k->iommu_enabled = virtio_pci_iommu_enabled;
+    k->ats_capable = virtio_pci_ats_capable;
     k->queue_enabled = virtio_pci_queue_enabled;
 }
 
-- 
2.35.3