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

From: Shameerali Kolothum Thodi
Date: Fri Sep 24 2021 - 03:44:46 EST

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> -----Original Message-----
> From: Max Gurtovoy [mailto:mgurtovoy@xxxxxxxxxx]
> Sent: 23 September 2021 14:56
> To: Leon Romanovsky <leon@xxxxxxxxxx>; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>
> Cc: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe
> <jgg@xxxxxxxxxx>; 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: 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@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
>
> 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.

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

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