linux-kernel - Re: [PATCH v6 3/4] vhost-vdpa: uAPI to suspend the device

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Date:   Tue, 28 Jun 2022 15:44:46 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Eugenio Pérez <eperezma@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>, Jason Wang <jasowang@...hat.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        kvm <kvm@...r.kernel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Cindy Lu <lulu@...hat.com>,
        "Kamde, Tanuj" <tanuj.kamde@....com>,
        Si-Wei Liu <si-wei.liu@...cle.com>, Piotr.Uminski@...el.com,
        habetsm.xilinx@...il.com, "Dawar, Gautam" <gautam.dawar@....com>,
        Pablo Cascon Katchadourian <pabloc@...inx.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>,
        Laurent Vivier <lvivier@...hat.com>,
        Longpeng <longpeng2@...wei.com>,
        Dinan Gunawardena <dinang@...inx.com>,
        Martin Petrus Hubertus Habets <martinh@...inx.com>,
        Martin Porter <martinpo@...inx.com>,
        Eli Cohen <elic@...dia.com>, ecree.xilinx@...il.com,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Harpreet Singh Anand <hanand@...inx.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Zhang Min <zhang.min9@....com.cn>
Subject: Re: [PATCH v6 3/4] vhost-vdpa: uAPI to suspend the device

On Thu, Jun 23, 2022 at 06:07:37PM +0200, Eugenio Pérez wrote:
>The ioctl adds support for suspending the device from userspace.
>
>This is a must before getting virtqueue indexes (base) for live migration,
>since the device could modify them after userland gets them. There are
>individual ways to perform that action for some devices
>(VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
>way to perform it for any vhost device (and, in particular, vhost-vdpa).
>
>After a successful return of the ioctl call the device must not process
>more virtqueue descriptors. The device can answer to read or writes of
>config fields as if it were not suspended. In particular, writing to
>"queue_enable" with a value of 1 will not make the device start
>processing buffers of the virtqueue.
>
>Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
>---
> drivers/vhost/vdpa.c       | 19 +++++++++++++++++++
> include/uapi/linux/vhost.h | 14 ++++++++++++++
> 2 files changed, 33 insertions(+)
>
>diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>index 3d636e192061..7fa671ac4bdf 100644
>--- a/drivers/vhost/vdpa.c
>+++ b/drivers/vhost/vdpa.c
>@@ -478,6 +478,22 @@ static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
>       return 0;
> }
>
>+/* After a successful return of ioctl the device must not process more
>+ * virtqueue descriptors. The device can answer to read or writes of config
>+ * fields as if it were not suspended. In particular, writing to "queue_enable"
>+ * with a value of 1 will not make the device start processing buffers.
>+ */
>+static long vhost_vdpa_suspend(struct vhost_vdpa *v)
>+{
>+      struct vdpa_device *vdpa = v->vdpa;
>+      const struct vdpa_config_ops *ops = vdpa->config;
>+
>+      if (!ops->suspend)
>+              return -EOPNOTSUPP;
>+
>+      return ops->suspend(vdpa);
>+}
>+
> static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>                                  void __user *argp)
> {
>@@ -654,6 +670,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>       case VHOST_VDPA_GET_VQS_COUNT:
>               r = vhost_vdpa_get_vqs_count(v, argp);
>               break;
>+      case VHOST_VDPA_SUSPEND:
>+              r = vhost_vdpa_suspend(v);
>+              break;
>       default:
>               r = vhost_dev_ioctl(&v->vdev, cmd, argp);
>               if (r == -ENOIOCTLCMD)
>diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
>index cab645d4a645..6d9f45163155 100644
>--- a/include/uapi/linux/vhost.h
>+++ b/include/uapi/linux/vhost.h
>@@ -171,4 +171,18 @@
> #define VHOST_VDPA_SET_GROUP_ASID     _IOW(VHOST_VIRTIO, 0x7C, \
>                                            struct vhost_vring_state)
>
>+/* Suspend or resume a device so it does not process virtqueue requests anymore
>+ *
>+ * After the return of ioctl with suspend != 0, the device must finish any
>+ * pending operations like in flight requests. It must also preserve all the
>+ * necessary state (the virtqueue vring base plus the possible device specific
>+ * states) that is required for restoring in the future. The device must not
>+ * change its configuration after that point.
>+ *
>+ * After the return of ioctl with suspend == 0, the device can continue
>+ * processing buffers as long as typical conditions are met (vq is enabled,
>+ * DRIVER_OK status bit is enabled, etc).
>+ */
>+#define VHOST_VDPA_SUSPEND            _IOW(VHOST_VIRTIO, 0x7D, int)
                                         ^
IIUC we are not using the argument anymore, so this should be changed in
_IO(VHOST_VIRTIO, 0x7D).

And we should update a bit the documentation.

Thanks,
Stefano