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

[Jason Wang]

On Sat, May 20, 2023 at 1:50 AM Viktor Prutyanov <viktor@daynix.com> wrote:
>
> On Thu, May 18, 2023 at 9:14 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > 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?
>
> It works for virtio-iommu because Linux guest doesn't enable PCI ATS in
> this situation. From my point of view, this fallback is not needed
> anymore, because it triggers only if Device-TLB isn't available on the
> host side but the guest misbehaves and tries to enable it.

Ok.

>
> Also, I would like to discuss two more points:
>
> 1. The patch series in its current form will fix the issue for
> vhost+iommu setup for any VirtIO device with any vhost backend when
> ATS is enabled at the beginning. But if ATS is enabled/disabled in the
> runtime it will only work for virtio-net with vhost-kernel. All other
> devices and backends are out of scope and will need to add almost the
> same device_iotlb_toggle and vhost_device_iotlb_toggle handlers. Since
> the issue is general for any device and any backend, is it normal from
> architectural point of view?

Yes, so I think it's better to fix others vhost backends. Actually I
wonder if we can have simply reuse vhost_toggle_device_iotlb() since
it's nothing specific to the vhost backend. It's just about the way to
receive IOTLB invalidation from vIOMMU.

>
> 2. When the series will be applied, we should enable DMA remapping for
> new Windows guest drivers, such as NetKVM. But if the user with enabled
> vhost+iommu updated the driver with old QEMU, the bug would reappear,
> because the guest doesn't know that the fix isn't present. May be we
> should discuss some mechanism to report that host is aware of guest's
> accept/reject of ATS/Device-TLB?

I'm not sure how this can help? Or anything makes this fix different
from other fixes?

One thing I can think is to backport the fixes to -stable.

Thanks

>
> Thanks,
> Viktor Prutyanov
>
> >
> > 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
> > >
> >
>