-----Original Message-----
From: Leon Romanovsky [mailto:leon@kernel.org]
Sent: 22 September 2021 11:39
To: Doug Ledford <redacted>; Jason Gunthorpe <jgg@nvidia.com>
Cc: Yishai Hadas <yishaih@nvidia.com>; Alex Williamson
[off-list ref]; Bjorn Helgaas [off-list ref]; David
S. Miller [off-list ref]; Jakub Kicinski [off-list ref]; Kirti
Wankhede [off-list ref]; kvm@vger.kernel.org;
linux-kernel@vger.kernel.org; linux-pci@vger.kernel.org;
linux-rdma@vger.kernel.org; netdev@vger.kernel.org; Saeed Mahameed
[off-list ref]
Subject: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
transition validity

From: Yishai Hadas <yishaih@nvidia.com>

Add an API in the core layer to check migration state transition validity
as part of a migration flow.

The valid transitions follow the expected usage as described in
uapi/vfio.h and triggered by QEMU.

This ensures that all migration implementations follow a consistent
migration state machine.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/vfio/vfio.c  | 41 +++++++++++++++++++++++++++++++++++++++++
 include/linux/vfio.h |  1 +
 2 files changed, 42 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 3c034fe14ccb..c3ca33e513c8 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c

@@ -1664,6 +1664,47 @@ static int vfio_device_fops_release(struct inode

*inode, struct file *filep)
 	return 0;
 }

+/**
+ * vfio_change_migration_state_allowed - Checks whether a migration state
+ *   transition is valid.
+ * @new_state: The new state to move to.
+ * @old_state: The old state.
+ * Return: true if the transition is valid.
+ */
+bool vfio_change_migration_state_allowed(u32 new_state, u32 old_state)
+{
+	enum { MAX_STATE = VFIO_DEVICE_STATE_RESUMING };
+	static const u8 vfio_from_state_table[MAX_STATE + 1][MAX_STATE + 1] = {
+		[VFIO_DEVICE_STATE_STOP] = {
+			[VFIO_DEVICE_STATE_RUNNING] = 1,
+			[VFIO_DEVICE_STATE_RESUMING] = 1,
+		},
+		[VFIO_DEVICE_STATE_RUNNING] = {
+			[VFIO_DEVICE_STATE_STOP] = 1,
+			[VFIO_DEVICE_STATE_SAVING] = 1,
+			[VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RUNNING]
= 1,

+		},
+		[VFIO_DEVICE_STATE_SAVING] = {
+			[VFIO_DEVICE_STATE_STOP] = 1,
+			[VFIO_DEVICE_STATE_RUNNING] = 1,
+		},
+		[VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RUNNING] = {
+			[VFIO_DEVICE_STATE_RUNNING] = 1,
+			[VFIO_DEVICE_STATE_SAVING] = 1,
+		},
+		[VFIO_DEVICE_STATE_RESUMING] = {
+			[VFIO_DEVICE_STATE_RUNNING] = 1,
+			[VFIO_DEVICE_STATE_STOP] = 1,
+		},
+	};
+
+	if (new_state > MAX_STATE || old_state > MAX_STATE)
+		return false;
+
+	return vfio_from_state_table[old_state][new_state];
+}
+EXPORT_SYMBOL_GPL(vfio_change_migration_state_allowed);
+
 static long vfio_device_fops_unl_ioctl(struct file *filep,
 				       unsigned int cmd, unsigned long arg)
 {

diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index b53a9557884a..e65137a708f1 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h

@@ -83,6 +83,7 @@ extern struct vfio_device

*vfio_device_get_from_dev(struct device *dev);
 extern void vfio_device_put(struct vfio_device *device);

 int vfio_assign_device_set(struct vfio_device *device, void *set_id);
+bool vfio_change_migration_state_allowed(u32 new_state, u32 old_state);

 /* events for the backend driver notify callback */
 enum vfio_iommu_notify_type {
--
2.31.1