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: Max Gurtovoy [mailto:mgurtovoy@nvidia.com]
> Sent: 27 September 2021 19:24
> 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 9/26/2021 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 ?

It is by the assumption that the default state to be _RUNNING and then
we take it from there for migration state changes.

Any particular reason why it needs to be in _STOP state? We need to update
the documentation in that case to allow _STOP --> _RESUMING.

> 
> >
> > 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