Re: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets disabled

[Laurent Vivier]

On 20/01/2025 18:33, Eric Auger wrote:
When a guest exposed with a vhost device and protected by an
intel IOMMU gets rebooted, we sometimes observe a spurious warning:
Fail to lookup the translated address ffffe000

We observe that the IOMMU gets disabled through a write to the global
command register (CMAR_GCMD.TE) before the vhost device gets stopped.
When this warning happens it can be observed an inflight IOTLB
miss occurs after the IOMMU disable and before the vhost stop. In
that case a flat translation occurs and the check in
vhost_memory_region_lookup() fails.

Let's disable the IOTLB callbacks when all IOMMU MRs have been
unregistered.

Signed-off-by: Eric Auger <eric.au...@redhat.com>
---
  hw/virtio/vhost.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 6aa72fd434..128c2ab094 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -931,6 +931,10 @@ static void vhost_iommu_region_del(MemoryListener 
*listener,
              break;
          }
      }
+    if (QLIST_EMPTY(&dev->iommu_list) &&
+        dev->vhost_ops->vhost_set_iotlb_callback) {
+        dev->vhost_ops->vhost_set_iotlb_callback(dev, false);
+    }
  }
  
  void vhost_toggle_device_iotlb(VirtIODevice *vdev)

I think you need the counterpart in vhost_iommu_region_del() (for instance if we have an 
add after a del that results in an empty list).
But you cannot unconditionally enable it (for instance if vhost is not started)

Perhaps you should move the vhost_set_iotlb_callback() call from 
vhost_start()/vhost_stop() to vhost_iommu_region_add()/vhost_iommu_region_del()?

Thanks,
Laurent