linux-kernel - Re: [PATCH RFC 3/4] vhost-vdpa: should restore 1:1 dma mapping before detaching driver

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Date:   Tue, 15 Aug 2023 10:32:03 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     eperezma@...hat.com, gal@...dia.com, linux-kernel@...r.kernel.org,
        mst@...hat.com, virtualization@...ts.linux-foundation.org,
        xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH RFC 3/4] vhost-vdpa: should restore 1:1 dma mapping before
 detaching driver

On Tue, Aug 15, 2023 at 9:45 AM Si-Wei Liu <si-wei.liu@...cle.com> wrote:
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
> ---
>  drivers/vhost/vdpa.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index b43e868..62b0a01 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -131,6 +131,15 @@ static struct vhost_vdpa_as *vhost_vdpa_find_alloc_as(struct vhost_vdpa *v,
>         return vhost_vdpa_alloc_as(v, asid);
>  }
>
> +static void vhost_vdpa_reset_map(struct vhost_vdpa *v, u32 asid)
> +{
> +       struct vdpa_device *vdpa = v->vdpa;
> +       const struct vdpa_config_ops *ops = vdpa->config;
> +
> +       if (ops->reset_map)
> +               ops->reset_map(vdpa, asid);
> +}
> +
>  static int vhost_vdpa_remove_as(struct vhost_vdpa *v, u32 asid)
>  {
>         struct vhost_vdpa_as *as = asid_to_as(v, asid);
> @@ -140,6 +149,14 @@ static int vhost_vdpa_remove_as(struct vhost_vdpa *v, u32 asid)
>
>         hlist_del(&as->hash_link);
>         vhost_vdpa_iotlb_unmap(v, &as->iotlb, 0ULL, 0ULL - 1, asid);
> +       /*
> +        * Devices with on-chip IOMMU need to restore iotlb
> +        * to 1:1 identity mapping before vhost-vdpa is going
> +        * to be removed and detached from the device. Give
> +        * them a chance to do so, as this cannot be done
> +        * efficiently via the whole-range unmap call above.
> +        */

Same question as before, if 1:1 is restored and the userspace doesn't
do any IOTLB updating. It looks like a security issue? (Assuming IOVA
is PA)

Thanks

> +       vhost_vdpa_reset_map(v, asid);
>         kfree(as);
>
>         return 0;
> --
> 1.8.3.1
>