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

[Leon Romanovsky]

On Thu, Sep 23, 2021 at 10:33:10AM +0000, Shameerali Kolothum Thodi wrote:
> 
> 
> > -----Original Message-----
> > From: Leon Romanovsky [mailto:leon@xxxxxxxxxx]
> > Sent: 22 September 2021 11:39
> > To: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Cc: Yishai Hadas <yishaih@xxxxxxxxxx>; Alex Williamson
> > <alex.williamson@xxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; David
> > S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Kirti
> > Wankhede <kwankhede@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > linux-rdma@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Saeed Mahameed
> > <saeedm@xxxxxxxxxx>
> > Subject: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
> > transition validity
> > 
> > From: Yishai Hadas <yishaih@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxx>
> > Reviewed-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
> > Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
> > ---
> >  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

> 
> " * 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
>