linux-kernel - Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

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Date:   Tue, 28 Jun 2022 15:43:40 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Eugenio Pérez <eperezma@...hat.com>
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        lulu@...hat.com, tanuj.kamde@....com,
        Si-Wei Liu <si-wei.liu@...cle.com>, Piotr.Uminski@...el.com,
        habetsm.xilinx@...il.com, gautam.dawar@....com, pabloc@...inx.com,
        Zhu Lingshan <lingshan.zhu@...el.com>, lvivier@...hat.com,
        Longpeng <longpeng2@...wei.com>, dinang@...inx.com,
        martinh@...inx.com, martinpo@...inx.com,
        Eli Cohen <elic@...dia.com>, ecree.xilinx@...il.com,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Dan Carpenter <dan.carpenter@...cle.com>, hanand@...inx.com,
        Xie Yongji <xieyongji@...edance.com>,
        Zhang Min <zhang.min9@....com.cn>
Subject: Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

On Thu, Jun 23, 2022 at 06:07:36PM +0200, Eugenio Pérez wrote:
>Userland knows if it can suspend the device or not by checking this feature
>bit.
>
>It's only offered if the vdpa driver backend implements the suspend()
>operation callback, and to offer it or userland to ack it if the backend
>does not offer that callback is an error.

Should we document in the previous patch that the callback must be 
implemented only if the drive/device support it?

The rest LGTM although I have a doubt whether it is better to move this 
patch after patch 3, or merge it with patch 3, for bisectability since 
we enable the feature here but if the userspace calls ioctl() with 
VHOST_VDPA_SUSPEND we reply back that it is not supported.

Thanks,
Stefano

>
>Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
>---
> drivers/vhost/vdpa.c             | 16 +++++++++++++++-
> include/uapi/linux/vhost_types.h |  2 ++
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>index 23dcbfdfa13b..3d636e192061 100644
>--- a/drivers/vhost/vdpa.c
>+++ b/drivers/vhost/vdpa.c
>@@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> 	return 0;
> }
>
>+static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
>+{
>+	struct vdpa_device *vdpa = v->vdpa;
>+	const struct vdpa_config_ops *ops = vdpa->config;
>+
>+	return ops->suspend;
>+}
>+
> static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> {
> 	struct vdpa_device *vdpa = v->vdpa;
>@@ -577,7 +585,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 	if (cmd == VHOST_SET_BACKEND_FEATURES) {
> 		if (copy_from_user(&features, featurep, sizeof(features)))
> 			return -EFAULT;
>-		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
>+		if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
>+				 BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
>+			return -EOPNOTSUPP;
>+		if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
>+		     !vhost_vdpa_can_suspend(v))
> 			return -EOPNOTSUPP;
> 		vhost_set_backend_features(&v->vdev, features);
> 		return 0;
>@@ -628,6 +640,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 		break;
> 	case VHOST_GET_BACKEND_FEATURES:
> 		features = VHOST_VDPA_BACKEND_FEATURES;
>+		if (vhost_vdpa_can_suspend(v))
>+			features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> 		if (copy_to_user(featurep, &features, sizeof(features)))
> 			r = -EFAULT;
> 		break;
>diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
>index 634cee485abb..1bdd6e363f4c 100644
>--- a/include/uapi/linux/vhost_types.h
>+++ b/include/uapi/linux/vhost_types.h
>@@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
>  * message
>  */
> #define VHOST_BACKEND_F_IOTLB_ASID  0x3
>+/* Device can be suspended */
>+#define VHOST_BACKEND_F_SUSPEND  0x4
>
> #endif
>-- 
>2.31.1
>