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

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 9/23/2021 2:17 PM, Leon Romanovsky wrote:
> On Thu, Sep 23, 2021 at 10:33:10AM +0000, Shameerali Kolothum Thodi wrote:
>>
>>> -----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,
> 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 ?

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


>
>> " * 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