Re: [RFC PATCH v2 3/4] vhost: register and change IOMMU flag depending on Device-TLB state

[Jason Wang]

On Mon, May 8, 2023 at 1:25 PM Jason Wang <jasowang@redhat.com> wrote:
>
> On Mon, May 1, 2023 at 10:02 AM 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                 | 26 ++++++++++++++++++++++++--
> >  include/hw/virtio/vhost-backend.h |  4 ++++
> >  include/hw/virtio/vhost.h         |  1 +
> >  4 files changed, 35 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > index 8e581575c9..30eb71fb83 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, int 
> > enable)
> > +{
> > +    vhost_toggle_device_iotlb(dev, enable);
> > +}
> > +
> >  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 a266396576..1bfcc6d263 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -796,7 +796,9 @@ 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);
> > @@ -804,7 +806,8 @@ 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);
> > +    ret = memory_region_register_iommu_notifier(section->mr, &iommu->n,
> > +            dev->vdev->device_iotlb_enabled ? NULL : &error_fatal);
> >      if (ret) {
> >          /*
> >           * Some vIOMMUs do not support dev-iotlb yet.  If so, try to use 
> > the
> > @@ -841,6 +844,25 @@ static void vhost_iommu_region_del(MemoryListener 
> > *listener,
> >      }
> >  }
> >
> > +void vhost_toggle_device_iotlb(struct vhost_dev *dev, bool enable)
> > +{
> > +    struct vhost_iommu *iommu;
> > +    int ret;
> > +
> > +    QLIST_FOREACH(iommu, &dev->iommu_list, iommu_next) {
> > +        memory_region_unregister_iommu_notifier(iommu->mr, &iommu->n);
> > +        iommu->n.notifier_flags = enable ?
> > +                IOMMU_NOTIFIER_DEVIOTLB_UNMAP : IOMMU_NOTIFIER_UNMAP;
> > +        ret = memory_region_register_iommu_notifier(iommu->mr, &iommu->n,
> > +                enable ? NULL : &error_fatal);
> > +        if (ret) {
> > +            iommu->n.notifier_flags = IOMMU_NOTIFIER_UNMAP;
> > +            memory_region_register_iommu_notifier(iommu->mr, &iommu->n,
> > +                                                  &error_fatal);
>
> I think it's better to tweak the code to avoid doing IOMMU_NOTIFIER_UNMAP 
> twice.
>
> The rest looks good.

Btw, it might worth to add comment to explain why we need this fallback.

Actually, I'm not sure I understand the logic.

E.g if guest tries to enable ATS it means it knows there's a vIOMMU
that support device IOTLB. If we use UNMAP notifier, we will lose the
device device IOTLB event here?

Thanks

>
> Thanks
>
> > +        }
> > +    }
> > +}
> > +
> >  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..f8e9660a96 100644
> > --- a/include/hw/virtio/vhost-backend.h
> > +++ b/include/hw/virtio/vhost-backend.h
> > @@ -133,6 +133,9 @@ 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,
> > +                                             int enabled);
> > +
> >  typedef struct VhostOps {
> >      VhostBackendType backend_type;
> >      vhost_backend_init vhost_backend_init;
> > @@ -181,6 +184,7 @@ 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..b3f585c6cd 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, bool enable);
> >  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
> >