linux-kernel - Re: [PATCH 2/4] vhost-vdpa: reset vendor specific mapping to initial state in .release

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Message-ID: <CAJaqyWe=RwotkcNKFuStvX=HxQh6sdtfsH23jhf994eXi3-2Og@mail.gmail.com>
Date:   Wed, 11 Oct 2023 13:21:46 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     jasowang@...hat.com, mst@...hat.com, xuanzhuo@...ux.alibaba.com,
        dtatulea@...dia.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] vhost-vdpa: reset vendor specific mapping to initial
 state in .release

On Tue, Oct 10, 2023 at 11:05 AM Si-Wei Liu <si-wei.liu@...cle.com> wrote:
>
> Devices with on-chip IOMMU or vendor specific IOTLB implementation
> may need to restore iotlb mapping to the initial or default state
> using the .reset_map op, as it's desirable for some parent devices
> to solely manipulate mappings by its own, independent of virtio device
> state. For instance, device reset does not cause mapping go away on
> such IOTLB model in need of persistent mapping. Before vhost-vdpa
> is going away, give them a chance to reset iotlb back to the initial
> state in vhost_vdpa_cleanup().
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
> ---
>  drivers/vhost/vdpa.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 851535f..a3f8160 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 +149,13 @@ 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);

Now I'm wondering, does this call to vhost_vdpa_iotlb_unmap sets a
different map (via .set_map) per element of the vhost_iotlb_itree? Not
a big deal since we're in the cleanup path, but it could be a nice
optimization on top as we're going to reset the map of the asid
anyway.

> +       /*
> +        * Devices with vendor specific IOMMU may need to restore
> +        * iotlb to the initial or default state which is not done
> +        * through device reset, as the IOTLB mapping manipulation
> +        * could be decoupled from the virtio device life cycle.
> +        */
> +       vhost_vdpa_reset_map(v, asid);
>         kfree(as);
>
>         return 0;
> --
> 1.8.3.1
>