Re: [PATCH v3 2/3] vhost: register and change IOMMU flag depending on Device-TLB state

[Jason Wang <jasowang@redhat.com>]

On Fri, May 12, 2023 at 9:51 PM Viktor Prutyanov <viktor@daynix.com> wrote:
>
> The guest can disable or never enable Device-TLB. In these cases,
> it can't be used even if enabled in QEMU. So, check Device-TLB state
> before registering IOMMU notifier and select unmap flag depending on
> that. Also, implement a way to change IOMMU notifier flag if Device-TLB
> state is changed.
>
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2001312
> Signed-off-by: Viktor Prutyanov <viktor@daynix.com>
> ---
>  hw/virtio/vhost-backend.c         |  6 ++++++
>  hw/virtio/vhost.c                 | 30 ++++++++++++++++++------------
>  include/hw/virtio/vhost-backend.h |  3 +++
>  include/hw/virtio/vhost.h         |  1 +
>  4 files changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index 8e581575c9..d39bfefd2d 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -297,6 +297,11 @@ static void vhost_kernel_set_iotlb_callback(struct vhost_dev *dev,
>          qemu_set_fd_handler((uintptr_t)dev->opaque, NULL, NULL, NULL);
>  }
>
> +static void vhost_kernel_toggle_device_iotlb(struct vhost_dev *dev)
> +{
> +    vhost_toggle_device_iotlb(dev);
> +}
> +
>  const VhostOps kernel_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_KERNEL,
>          .vhost_backend_init = vhost_kernel_init,
> @@ -328,6 +333,7 @@ const VhostOps kernel_ops = {
>          .vhost_vsock_set_running = vhost_kernel_vsock_set_running,
>          .vhost_set_iotlb_callback = vhost_kernel_set_iotlb_callback,
>          .vhost_send_device_iotlb_msg = vhost_kernel_send_device_iotlb_msg,
> +        .vhost_toggle_device_iotlb = vhost_kernel_toggle_device_iotlb,
>  };
>  #endif
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 746d130c74..41c9fbf286 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -781,7 +781,6 @@ 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;
> @@ -796,7 +795,9 @@ static void vhost_iommu_region_add(MemoryListener *listener,
>      iommu_idx = memory_region_iommu_attrs_to_index(iommu_mr,
>                                                     MEMTXATTRS_UNSPECIFIED);
>      iommu_notifier_init(&iommu->n, vhost_iommu_unmap_notify,
> -                        IOMMU_NOTIFIER_DEVIOTLB_UNMAP,
> +                        dev->vdev->device_iotlb_enabled ?
> +                            IOMMU_NOTIFIER_DEVIOTLB_UNMAP :
> +                            IOMMU_NOTIFIER_UNMAP,
>                          section->offset_within_region,
>                          int128_get64(end),
>                          iommu_idx);
> @@ -804,16 +805,8 @@ 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);
> -    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);
> -    }

So we lose this fallback. Is this really intended?

E.g does it work if you are using virtio-iommu?

Thanks

> +    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? */
>  }
> @@ -841,6 +834,19 @@ static void vhost_iommu_region_del(MemoryListener *listener,
>      }
>  }
>
> +void vhost_toggle_device_iotlb(struct vhost_dev *dev)
> +{
> +    struct vhost_iommu *iommu;
> +
> +    QLIST_FOREACH(iommu, &dev->iommu_list, iommu_next) {
> +        memory_region_unregister_iommu_notifier(iommu->mr, &iommu->n);
> +        iommu->n.notifier_flags = dev->vdev->device_iotlb_enabled ?
> +                IOMMU_NOTIFIER_DEVIOTLB_UNMAP : IOMMU_NOTIFIER_UNMAP;
> +        memory_region_register_iommu_notifier(iommu->mr, &iommu->n,
> +                                              &error_fatal);
> +    }
> +}
> +
>  static int vhost_virtqueue_set_addr(struct vhost_dev *dev,
>                                      struct vhost_virtqueue *vq,
>                                      unsigned idx, bool enable_log)
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index ec3fbae58d..10a3c36b4b 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -133,6 +133,8 @@ typedef int (*vhost_set_config_call_op)(struct vhost_dev *dev,
>
>  typedef void (*vhost_reset_status_op)(struct vhost_dev *dev);
>
> +typedef void (*vhost_toggle_device_iotlb_op)(struct vhost_dev *dev);
> +
>  typedef struct VhostOps {
>      VhostBackendType backend_type;
>      vhost_backend_init vhost_backend_init;
> @@ -181,6 +183,7 @@ typedef struct VhostOps {
>      vhost_force_iommu_op vhost_force_iommu;
>      vhost_set_config_call_op vhost_set_config_call;
>      vhost_reset_status_op vhost_reset_status;
> +    vhost_toggle_device_iotlb_op vhost_toggle_device_iotlb;
>  } VhostOps;
>
>  int vhost_backend_update_device_iotlb(struct vhost_dev *dev,
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index a52f273347..785832ed46 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -320,6 +320,7 @@ bool vhost_has_free_slot(void);
>  int vhost_net_set_backend(struct vhost_dev *hdev,
>                            struct vhost_vring_file *file);
>
> +void vhost_toggle_device_iotlb(struct vhost_dev *dev);
>  int vhost_device_iotlb_miss(struct vhost_dev *dev, uint64_t iova, int write);
>
>  int vhost_virtqueue_start(struct vhost_dev *dev, struct VirtIODevice *vdev,
> --
> 2.35.1
>