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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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        Saeed Mahameed <saeedm@nvidia.com>,
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From:   Max Gurtovoy <mgurtovoy@nvidia.com>
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Date:   Sun, 26 Sep 2021 12:09:31 +0300
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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 ?


>
> 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