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

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Leon Romanovsky [mailto:leon@kernel.org]
> Sent: 22 September 2021 11:39
> To: Doug Ledford <dledford@redhat.com>; Jason Gunthorpe <jgg@nvidia.com>
> Cc: Yishai Hadas <yishaih@nvidia.com>; Alex Williamson
> <alex.williamson@redhat.com>; Bjorn Helgaas <bhelgaas@google.com>; David
> S. Miller <davem@davemloft.net>; Jakub Kicinski <kuba@kernel.org>; Kirti
> Wankhede <kwankhede@nvidia.com>; 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
> <saeedm@nvidia.com>
> 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,

Do we need to allow _RESUMING state here or not? As per the "State transitions"
section from uapi/linux/vfio.h, 

" * 4. To start the resuming phase, the device state should be transitioned from
 *    the _RUNNING to the _RESUMING state."

IIRC, I have seen that transition happening on the destination dev while testing the 
HiSilicon ACC dev migration. 

Thanks,
Shameer

> +		},
> +		[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