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Date:   Fri, 13 Jan 2023 11:13:45 +0100
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     sebastien.boeuf@intel.com
Cc:     linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, mst@redhat.com,
        jasowang@redhat.com, eperezma@redhat.com
Subject: Re: [PATCH v6 3/4] vhost-vdpa: uAPI to resume the device
Message-ID: <20230113101345.j7s7ecn2sozkd44s@sgarzare-redhat>
References: <cover.1672742878.git.sebastien.boeuf@intel.com>
 <73b75fb87d25cff59768b4955a81fe7ffe5b4770.1672742878.git.sebastien.boeuf@intel.com>
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On Tue, Jan 03, 2023 at 11:51:07AM +0100, sebastien.boeuf@intel.com wrote:
>From: Sebastien Boeuf <sebastien.boeuf@intel.com>
>
>This new ioctl adds support for resuming the device from userspace.
>
>This is required when trying to restore the device in a functioning
>state after it's been suspended. It is already possible to reset a
>suspended device, but that means the device must be reconfigured and
>all the IOMMU/IOTLB mappings must be recreated. This new operation
>allows the device to be resumed without going through a full reset.
>
>This is particularly useful when trying to perform offline migration of
>a virtual machine (also known as snapshot/restore) as it allows the VMM
>to resume the virtual machine back to a running state after the snapshot
>is performed.
>
>Acked-by: Jason Wang <jasowang@redhat.com>
>Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
>---
> drivers/vhost/vdpa.c       | 18 ++++++++++++++++++
> include/uapi/linux/vhost.h |  8 ++++++++
> 2 files changed, 26 insertions(+)
>
>diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>index 833617d00ef6..1db7bd39fb63 100644
>--- a/drivers/vhost/vdpa.c
>+++ b/drivers/vhost/vdpa.c
>@@ -502,6 +502,21 @@ static long vhost_vdpa_suspend(struct vhost_vdpa *v)
> 	return ops->suspend(vdpa);
> }
>
>+/* After a successful return of this ioctl the device resumes processing
>+ * virtqueue descriptors. The device becomes fully operational the same way it
>+ * was before it was suspended.
>+ */
>+static long vhost_vdpa_resume(struct vhost_vdpa *v)
>+{
>+	struct vdpa_device *vdpa = v->vdpa;
>+	const struct vdpa_config_ops *ops = vdpa->config;
>+
>+	if (!ops->resume)
>+		return -EOPNOTSUPP;
>+
>+	return ops->resume(vdpa);
>+}
>+
> static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
> 				   void __user *argp)
> {
>@@ -687,6 +702,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 	case VHOST_VDPA_SUSPEND:
> 		r = vhost_vdpa_suspend(v);
> 		break;
>+	case VHOST_VDPA_RESUME:
>+		r = vhost_vdpa_resume(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 f9f115a7c75b..92e1b700b51c 100644
>--- a/include/uapi/linux/vhost.h
>+++ b/include/uapi/linux/vhost.h
>@@ -180,4 +180,12 @@
>  */
> #define VHOST_VDPA_SUSPEND		_IO(VHOST_VIRTIO, 0x7D)
>
>+/* Resume a device so it can resume processing virtqueue requests
>+ *
>+ * After the return of this ioctl the device will have restored all the
>+ * necessary states and it is fully operational to continue processing the
>+ * virtqueue descriptors.

IIUC this is a no-op if the device wasn't suspended.
If you have to resend, maybe add this info also here in the user 
documentation.

Anyway, the patch LGTM:

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

>+ */
>+#define VHOST_VDPA_RESUME		_IO(VHOST_VIRTIO, 0x7E)
>+
> #endif
>-- 
>2.37.2
>
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