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

From: Shameerali Kolothum Thodi <[email-masked]>
Date: Sun, 26 Sep 2021 16:17:07 +0000

> -----Original Message-----
> From: Max Gurtovoy [mailto:[email-masked]]
> Sent: 26 September 2021 10:10
> To: Shameerali Kolothum Thodi <[email-masked]>;
> Leon Romanovsky <[email-masked]>
> Cc: Doug Ledford <[email-masked]>; Jason Gunthorpe
> <[email-masked]>; Yishai Hadas <[email-masked]>; Alex Williamson
> <[email-masked]>; Bjorn Helgaas <[email-masked]>; David
> S. Miller <[email-masked]>; Jakub Kicinski <[email-masked]>; Kirti
> Wankhede <[email-masked]>; [email-masked];
> [email-masked]; [email-masked];
> [email-masked]; [email-masked]; Saeed Mahameed
> <[email-masked]>; liulongfang <[email-masked]>
> 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:[email-masked]]
> >> Sent: 23 September 2021 14:56
> >> To: Leon Romanovsky <[email-masked]>; Shameerali Kolothum Thodi
> >> <[email-masked]>
> >> Cc: Doug Ledford <[email-masked]>; Jason Gunthorpe
> >> <[email-masked]>; Yishai Hadas <[email-masked]>; Alex Williamson
> >> <[email-masked]>; Bjorn Helgaas <[email-masked]>;
> >> David S. Miller <[email-masked]>; Jakub Kicinski
> >> <[email-masked]>; Kirti Wankhede <[email-masked]>;
> >> [email-masked]; [email-masked];
> >> [email-masked]; [email-masked];
> >> [email-masked]; Saeed Mahameed <[email-masked]>
> >> 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:[email-masked]]
> >>>>> Sent: 22 September 2021 11:39
> >>>>> To: Doug Ledford <[email-masked]>; Jason Gunthorpe
> >> <[email-masked]>
> >>>>> Cc: Yishai Hadas <[email-masked]>; Alex Williamson
> >>>>> <[email-masked]>; Bjorn Helgaas <[email-masked]>;
> >> David
> >>>>> S. Miller <[email-masked]>; Jakub Kicinski <[email-masked]>;
> >>>>> Kirti Wankhede <[email-masked]>; [email-masked];
> >>>>> [email-masked]; [email-masked];
> >>>>> [email-masked]; [email-masked]; Saeed Mahameed
> >>>>> <[email-masked]>
> >>>>> Subject: [PATCH mlx5-next 2/7] vfio: Add an API to check migration
> >>>>> state transition validity
> >>>>>
> >>>>> From: Yishai Hadas <[email-masked]>
> >>>>>
> >>>>> 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 <[email-masked]>
> >>>>> Reviewed-by: Kirti Wankhede <[email-masked]>
> >>>>> Signed-off-by: Jason Gunthorpe <[email-masked]>
> >>>>> Signed-off-by: Leon Romanovsky <[email-masked]>
> >>>>> ---
> >>>>>    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.

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