-----Original Message-----
From: Max Gurtovoy [mailto:mgurtovoy@nvidia.com]
Sent: 23 September 2021 14:56
To: Leon Romanovsky <leon@kernel.org>; Shameerali Kolothum Thodi
[off-list ref]
Cc: Doug Ledford <redacted>; Jason Gunthorpe
[off-list ref]; Yishai Hadas [off-list ref]; 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: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
transition validity


On 9/23/2021 2:17 PM, Leon Romanovsky wrote:

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On Thu, Sep 23, 2021 at 10:33:10AM +0000, Shameerali Kolothum Thodi

wrote:

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-----Original Message-----
From: Leon Romanovsky [mailto:leon@kernel.org]
Sent: 22 September 2021 11:39
To: Doug Ledford <redacted>; Jason Gunthorpe

[off-list ref]

quoted

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Cc: Yishai Hadas <yishaih@nvidia.com>; Alex Williamson
[off-list ref]; Bjorn Helgaas [off-list ref];

David

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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

+++++++++++++++++++++++++++++++++++++++++

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  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

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

+/**
+ * vfio_change_migration_state_allowed - Checks whether a migration

state

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+ *   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)

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+{
+	enum { MAX_STATE = VFIO_DEVICE_STATE_RESUMING };
+	static const u8 vfio_from_state_table[MAX_STATE + 1][MAX_STATE +

1] = {

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+		[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]

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= 1,

Do we need to allow _RESUMING state here or not? As per the "State

transitions"

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section from uapi/linux/vfio.h,

It looks like we missed this state transition.

Thanks

I'm not sure this state transition is valid.

Kirti, When we would like to move from RUNNING to RESUMING ?

I guess it depends on what you report as your dev default state. 

For HiSilicon ACC migration driver, we set the default to _RUNNING.

And when the migration starts, the destination side Qemu, set the 
device state to _RESUMING(vfio_load_state()).

From the documentation, it looks like the assumption on default state of
the VFIO dev is _RUNNING.

"
*  001b => Device running, which is the default state
"

Sameerali, can you please re-test and update if you see this transition ?

Yes. And if I change the default state to _STOP, then the transition
is from _STOP --> _RESUMING.

But the documentation on State transitions doesn't have _STOP --> _RESUMING
transition as valid.

Thanks,
Shameer 

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" * 4. To start the resuming phase, the device state should be transitioned

from

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  *    the _RUNNING to the _RESUMING state."

IIRC, I have seen that transition happening on the destination dev while

testing the

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HiSilicon ACC dev migration.

Thanks,
Shameer

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+		},
+		[VFIO_DEVICE_STATE_SAVING] = {
+			[VFIO_DEVICE_STATE_STOP] = 1,
+			[VFIO_DEVICE_STATE_RUNNING] = 1,
+		},
+		[VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RUNNING]

= {

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+			[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);

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