Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.33 as permitted sender) client-ip=23.128.96.33;
MIME-Version: 1.0
References: <20231205104609.876194-1-dtatulea@nvidia.com> <20231205104609.876194-5-dtatulea@nvidia.com>
 <CAJaqyWeEY9LNTE8QEnJgLhgS7HiXr5gJEwwPBrC3RRBsAE4_7Q@mail.gmail.com>
 <27312106-07b9-4719-970c-b8e1aed7c4eb@oracle.com> <075cf7d1ada0ee4ee30d46b993a1fe21acfe9d92.camel@nvidia.com>
 <20231214084526-mutt-send-email-mst@kernel.org> <9a6465a3d6c8fde63643fbbdde60d5dd84b921d4.camel@nvidia.com>
In-Reply-To: <9a6465a3d6c8fde63643fbbdde60d5dd84b921d4.camel@nvidia.com>
From:   Eugenio Perez Martin <eperezma@redhat.com>
Date:   Thu, 14 Dec 2023 19:30:44 +0100
Message-ID: <CAJaqyWfF9eVehQ+wutMDdwYToMq=G1+War_7wANmnyuONj=18g@mail.gmail.com>
Subject: Re: [PATCH vhost v2 4/8] vdpa/mlx5: Mark vq addrs for modification in
 hw vq
To:     Dragos Tatulea <dtatulea@nvidia.com>
Cc:     "mst@redhat.com" <mst@redhat.com>,
        "xuanzhuo@linux.alibaba.com" <xuanzhuo@linux.alibaba.com>,
        Parav Pandit <parav@nvidia.com>, Gal Pressman <gal@nvidia.com>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "si-wei.liu@oracle.com" <si-wei.liu@oracle.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        Saeed Mahameed <saeedm@nvidia.com>,
        "leon@kernel.org" <leon@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Dec 14, 2023 at 4:51=E2=80=AFPM Dragos Tatulea <dtatulea@nvidia.com=
> wrote:
>
> On Thu, 2023-12-14 at 08:45 -0500, Michael S. Tsirkin wrote:
> > On Thu, Dec 14, 2023 at 01:39:55PM +0000, Dragos Tatulea wrote:
> > > On Tue, 2023-12-12 at 15:44 -0800, Si-Wei Liu wrote:
> > > >
> > > > On 12/12/2023 11:21 AM, Eugenio Perez Martin wrote:
> > > > > On Tue, Dec 5, 2023 at 11:46=E2=80=AFAM Dragos Tatulea <dtatulea@=
nvidia.com> wrote:
> > > > > > Addresses get set by .set_vq_address. hw vq addresses will be u=
pdated on
> > > > > > next modify_virtqueue.
> > > > > >
> > > > > > Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> > > > > > Reviewed-by: Gal Pressman <gal@nvidia.com>
> > > > > > Acked-by: Eugenio P=C3=A9rez <eperezma@redhat.com>
> > > > > I'm kind of ok with this patch and the next one about state, but =
I
> > > > > didn't ack them in the previous series.
> > > > >
> > > > > My main concern is that it is not valid to change the vq address =
after
> > > > > DRIVER_OK in VirtIO, which vDPA follows. Only memory maps are ok =
to
> > > > > change at this moment. I'm not sure about vq state in vDPA, but v=
host
> > > > > forbids changing it with an active backend.
> > > > >
> > > > > Suspend is not defined in VirtIO at this moment though, so maybe =
it is
> > > > > ok to decide that all of these parameters may change during suspe=
nd.
> > > > > Maybe the best thing is to protect this with a vDPA feature flag.
> > > > I think protect with vDPA feature flag could work, while on the oth=
er
> > > > hand vDPA means vendor specific optimization is possible around sus=
pend
> > > > and resume (in case it helps performance), which doesn't have to be
> > > > backed by virtio spec. Same applies to vhost user backend features,
> > > > variations there were not backed by spec either. Of course, we shou=
ld
> > > > try best to make the default behavior backward compatible with
> > > > virtio-based backend, but that circles back to no suspend definitio=
n in
> > > > the current virtio spec, for which I hope we don't cease developmen=
t on
> > > > vDPA indefinitely. After all, the virtio based vdap backend can wel=
l
> > > > define its own feature flag to describe (minor difference in) the
> > > > suspend behavior based on the later spec once it is formed in futur=
e.
> > > >
> > > So what is the way forward here? From what I understand the options a=
re:
> > >
> > > 1) Add a vdpa feature flag for changing device properties while suspe=
nded.
> > >
> > > 2) Drop these 2 patches from the series for now. Not sure if this mak=
es sense as
> > > this. But then Si-Wei's qemu device suspend/resume poc [0] that exerc=
ises this
> > > code won't work anymore. This means the series would be less well tes=
ted.
> > >
> > > Are there other possible options? What do you think?
> > >
> > > [0] https://github.com/siwliu-kernel/qemu/tree/svq-resume-wip
> >
> > I am fine with either of these.
> >
> How about allowing the change only under the following conditions:
>   vhost_vdpa_can_suspend && vhost_vdpa_can_resume &&
> VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is set
>
> ?

I think the best option by far is 1, as there is no hint in the
combination of these 3 indicating that you can change device
properties in the suspended state.

>
> Thanks,
> Dragos
>
> > > Thanks,
> > > Dragos
> > >
> > > > Regards,
> > > > -Siwei
> > > >
> > > >
> > > >
> > > > >
> > > > > Jason, what do you think?
> > > > >
> > > > > Thanks!
> > > > >
> > > > > > ---
> > > > > >   drivers/vdpa/mlx5/net/mlx5_vnet.c  | 9 +++++++++
> > > > > >   include/linux/mlx5/mlx5_ifc_vdpa.h | 1 +
> > > > > >   2 files changed, 10 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/m=
lx5/net/mlx5_vnet.c
> > > > > > index f8f088cced50..80e066de0866 100644
> > > > > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > > > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > > > > @@ -1209,6 +1209,7 @@ static int modify_virtqueue(struct mlx5_v=
dpa_net *ndev,
> > > > > >          bool state_change =3D false;
> > > > > >          void *obj_context;
> > > > > >          void *cmd_hdr;
> > > > > > +       void *vq_ctx;
> > > > > >          void *in;
> > > > > >          int err;
> > > > > >
> > > > > > @@ -1230,6 +1231,7 @@ static int modify_virtqueue(struct mlx5_v=
dpa_net *ndev,
> > > > > >          MLX5_SET(general_obj_in_cmd_hdr, cmd_hdr, uid, ndev->m=
vdev.res.uid);
> > > > > >
> > > > > >          obj_context =3D MLX5_ADDR_OF(modify_virtio_net_q_in, i=
n, obj_context);
> > > > > > +       vq_ctx =3D MLX5_ADDR_OF(virtio_net_q_object, obj_contex=
t, virtio_q_context);
> > > > > >
> > > > > >          if (mvq->modified_fields & MLX5_VIRTQ_MODIFY_MASK_STAT=
E) {
> > > > > >                  if (!is_valid_state_change(mvq->fw_state, stat=
e, is_resumable(ndev))) {
> > > > > > @@ -1241,6 +1243,12 @@ static int modify_virtqueue(struct mlx5_=
vdpa_net *ndev,
> > > > > >                  state_change =3D true;
> > > > > >          }
> > > > > >
> > > > > > +       if (mvq->modified_fields & MLX5_VIRTQ_MODIFY_MASK_VIRTI=
O_Q_ADDRS) {
> > > > > > +               MLX5_SET64(virtio_q, vq_ctx, desc_addr, mvq->de=
sc_addr);
> > > > > > +               MLX5_SET64(virtio_q, vq_ctx, used_addr, mvq->de=
vice_addr);
> > > > > > +               MLX5_SET64(virtio_q, vq_ctx, available_addr, mv=
q->driver_addr);
> > > > > > +       }
> > > > > > +
> > > > > >          MLX5_SET64(virtio_net_q_object, obj_context, modify_fi=
eld_select, mvq->modified_fields);
> > > > > >          err =3D mlx5_cmd_exec(ndev->mvdev.mdev, in, inlen, out=
, sizeof(out));
> > > > > >          if (err)
> > > > > > @@ -2202,6 +2210,7 @@ static int mlx5_vdpa_set_vq_address(struc=
t vdpa_device *vdev, u16 idx, u64 desc_
> > > > > >          mvq->desc_addr =3D desc_area;
> > > > > >          mvq->device_addr =3D device_area;
> > > > > >          mvq->driver_addr =3D driver_area;
> > > > > > +       mvq->modified_fields |=3D MLX5_VIRTQ_MODIFY_MASK_VIRTIO=
_Q_ADDRS;
> > > > > >          return 0;
> > > > > >   }
> > > > > >
> > > > > > diff --git a/include/linux/mlx5/mlx5_ifc_vdpa.h b/include/linux=
/mlx5/mlx5_ifc_vdpa.h
> > > > > > index b86d51a855f6..9594ac405740 100644
> > > > > > --- a/include/linux/mlx5/mlx5_ifc_vdpa.h
> > > > > > +++ b/include/linux/mlx5/mlx5_ifc_vdpa.h
> > > > > > @@ -145,6 +145,7 @@ enum {
> > > > > >          MLX5_VIRTQ_MODIFY_MASK_STATE                    =3D (u=
64)1 << 0,
> > > > > >          MLX5_VIRTQ_MODIFY_MASK_DIRTY_BITMAP_PARAMS      =3D (u=
64)1 << 3,
> > > > > >          MLX5_VIRTQ_MODIFY_MASK_DIRTY_BITMAP_DUMP_ENABLE =3D (u=
64)1 << 4,
> > > > > > +       MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_ADDRS           =3D (u6=
4)1 << 6,
> > > > > >          MLX5_VIRTQ_MODIFY_MASK_DESC_GROUP_MKEY          =3D (u=
64)1 << 14,
> > > > > >   };
> > > > > >
> > > > > > --
> > > > > > 2.42.0
> > > > > >
> > > >
> > >
> >
>