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Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
 transition validity
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
        "Leon Romanovsky" <leon@kernel.org>
CC:     Doug Ledford <dledford@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Yishai Hadas <yishaih@nvidia.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "David S. Miller" <davem@davemloft.net>,
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        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Saeed Mahameed <saeedm@nvidia.com>,
        liulongfang <liulongfang@huawei.com>
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From:   Max Gurtovoy <mgurtovoy@nvidia.com>
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Date:   Mon, 27 Sep 2021 21:24:19 +0300
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On 9/26/2021 7:17 PM, Shameerali Kolothum Thodi wrote:
>
>> -----Original Message-----
>> From: Max Gurtovoy [mailto:mgurtovoy@nvidia.com]
>> Sent: 26 September 2021 10:10
>> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
>> Leon Romanovsky <leon@kernel.org>
>> Cc: Doug Ledford <dledford@redhat.com>; Jason Gunthorpe
>> <jgg@nvidia.com>; 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>; liulongfang <liulongfang@huawei.com>
>> Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
>> transition validity
>>
>>
>> On 9/24/2021 10:44 AM, Shameerali Kolothum Thodi wrote:
>>>> -----Original Message-----
>>>> From: Max Gurtovoy [mailto:mgurtovoy@nvidia.com]
>>>> Sent: 23 September 2021 14:56
>>>> To: Leon Romanovsky <leon@kernel.org>; Shameerali Kolothum Thodi
>>>> <shameerali.kolothum.thodi@huawei.com>
>>>> Cc: Doug Ledford <dledford@redhat.com>; Jason Gunthorpe
>>>> <jgg@nvidia.com>; 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: 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:
>>>>> 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 ?
>>> I guess it depends on what you report as your dev default state.
>>>
>>> For HiSilicon ACC migration driver, we set the default to _RUNNING.
>> Where do you set it and report it ?
> Currently, in _open_device() we set the device_state to _RUNNING.

Why do you do it ?

>
> I think in your case the default of vmig->vfio_dev_state == 0 (_STOP).
>
>>> 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
>>>
>>>>>> " * 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