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

[Duan, Zhenzhong]

Hi Eric,

>-----Original Message-----
>From: Eric Auger <eric.au...@redhat.com>
>Subject: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets
>disabled
>
>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

Do you see this print once during one time reboot?

>
>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.

Try to understand the sequence, is it like below?

           vhost                                                     vcpu       
   

call into vtd_iommu_translate();

                                                                    set 
s->dmar_enabled = false;
                                                                    switch off 
iommu address space;
                                                                    disable 
vhost IOTLB callbacks;

check if !s->dmar_enabled;
return flat translation and trigger warning

Thanks
Zhenzhong

>
>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)
>--
>2.47.1