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

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Date:   Fri, 13 Jan 2023 11:11:44 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     sebastien.boeuf@...el.com
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        jasowang@...hat.com, eperezma@...hat.com
Subject: Re: [PATCH v6 2/4] vhost-vdpa: Introduce RESUME backend feature bit

On Tue, Jan 03, 2023 at 11:51:06AM +0100, sebastien.boeuf@...el.com wrote:
>From: Sebastien Boeuf <sebastien.boeuf@...el.com>
>
>Userspace knows if the device can be resumed or not by checking this
>feature bit.
>
>It's only exposed if the vdpa driver backend implements the resume()
>operation callback. Userspace trying to negotiate this feature when it
>hasn't been exposed will result in an error.
>
>Acked-by: Jason Wang <jasowang@...hat.com>
>Signed-off-by: Sebastien Boeuf <sebastien.boeuf@...el.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 166044642fd5..833617d00ef6 100644
>--- a/drivers/vhost/vdpa.c
>+++ b/drivers/vhost/vdpa.c
>@@ -355,6 +355,14 @@ static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> 	return ops->suspend;
> }
>
>+static bool vhost_vdpa_can_resume(const struct vhost_vdpa *v)
>+{
>+	struct vdpa_device *vdpa = v->vdpa;
>+	const struct vdpa_config_ops *ops = vdpa->config;
>+
>+	return ops->resume;
>+}
>+
> static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> {
> 	struct vdpa_device *vdpa = v->vdpa;
>@@ -602,11 +610,15 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 		if (copy_from_user(&features, featurep, sizeof(features)))
> 			return -EFAULT;
> 		if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
>-				 BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
>+				 BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
>+				 BIT_ULL(VHOST_BACKEND_F_RESUME)))
> 			return -EOPNOTSUPP;
> 		if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> 		     !vhost_vdpa_can_suspend(v))
> 			return -EOPNOTSUPP;
>+		if ((features & BIT_ULL(VHOST_BACKEND_F_RESUME)) &&
>+		     !vhost_vdpa_can_resume(v))
>+			return -EOPNOTSUPP;

Not for this patch, but I'd like to refactor this code a bit to fill a 
`backend_features` field in vhost_vdpa during the vhost_vdpa_probe(), so 
we don't need to change this code or the VHOST_GET_BACKEND_FEATURES for 
every new backend feature.

I'll send a patch.

This LGTM:

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>


> 		vhost_set_backend_features(&v->vdev, features);
> 		return 0;
> 	}
>@@ -658,6 +670,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 		features = VHOST_VDPA_BACKEND_FEATURES;
> 		if (vhost_vdpa_can_suspend(v))
> 			features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
>+		if (vhost_vdpa_can_resume(v))
>+			features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
> 		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 53601ce2c20a..c5690a8992d8 100644
>--- a/include/uapi/linux/vhost_types.h
>+++ b/include/uapi/linux/vhost_types.h
>@@ -163,5 +163,7 @@ struct vhost_vdpa_iova_range {
> #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> /* Device can be suspended */
> #define VHOST_BACKEND_F_SUSPEND  0x4
>+/* Device can be resumed */
>+#define VHOST_BACKEND_F_RESUME  0x5
>
> #endif
>-- 
>2.37.2
>
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