linux-kernel - [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity

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Message-Id: <c87f55d6fec77a22b110d3c9611744e6b28bba46.1632305919.git.leonro@nvidia.com>
Date:   Wed, 22 Sep 2021 13:38:51 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     Yishai Hadas <yishaih@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Kirti Wankhede <kwankhede@...dia.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>
Subject: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity

From: Yishai Hadas <yishaih@...dia.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@...dia.com>
Reviewed-by: Kirti Wankhede <kwankhede@...dia.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Leon Romanovsky <leonro@...dia.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