On Thu, Feb 24 2022, Yishai Hadas <yishaih@xxxxxxxxxx> wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
>
> The RUNNING_P2P state is designed to support multiple devices in the same
> VM that are doing P2P transactions between themselves. When in RUNNING_P2P
> the device must be able to accept incoming P2P transactions but should not
> generate outgoing P2P transactions.
>
> As an optional extension to the mandatory states it is defined as
> inbetween STOP and RUNNING:
> STOP -> RUNNING_P2P -> RUNNING -> RUNNING_P2P -> STOP
>
> For drivers that are unable to support RUNNING_P2P the core code
> silently merges RUNNING_P2P and RUNNING together. Unless driver support
> is present, the new state cannot be used in SET_STATE.
> Drivers that support this will be required to implement 4 FSM arcs
> beyond the basic FSM. 2 of the basic FSM arcs become combination
> transitions.
>
> Compared to the v1 clarification, NDMA is redefined into FSM states and is
> described in terms of the desired P2P quiescent behavior, noting that
> halting all DMA is an acceptable implementation.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Signed-off-by: Yishai Hadas <yishaih@xxxxxxxxxx>
> ---
> drivers/vfio/vfio.c | 84 +++++++++++++++++++++++++++++++--------
> include/linux/vfio.h | 1 +
> include/uapi/linux/vfio.h | 36 ++++++++++++++++-
> 3 files changed, 102 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index b37ab27b511f..bdb5205bb358 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1577,39 +1577,55 @@ int vfio_mig_get_next_state(struct vfio_device *device,
> enum vfio_device_mig_state new_fsm,
> enum vfio_device_mig_state *next_fsm)
> {
> - enum { VFIO_DEVICE_NUM_STATES = VFIO_DEVICE_STATE_RESUMING + 1 };
> + enum { VFIO_DEVICE_NUM_STATES = VFIO_DEVICE_STATE_RUNNING_P2P + 1 };
> /*
> - * The coding in this table requires the driver to implement 6
> + * The coding in this table requires the driver to implement
> * FSM arcs:
Nit: this now reads a bit strange; maybe "requires the driver to
implement the following FSM arcs"?
> * RESUMING -> STOP
> - * RUNNING -> STOP
> * STOP -> RESUMING
> - * STOP -> RUNNING
> * STOP -> STOP_COPY
> * STOP_COPY -> STOP
> *
> - * The coding will step through multiple states for these combination
> - * transitions:
> - * RESUMING -> STOP -> RUNNING
> + * If P2P is supported then the driver must also implement these FSM
> + * arcs:
> + * RUNNING -> RUNNING_P2P
> + * RUNNING_P2P -> RUNNING
> + * RUNNING_P2P -> STOP
> + * STOP -> RUNNING_P2P
> + * Without P2P the driver must implement:
> + * RUNNING -> STOP
> + * STOP -> RUNNING
> + *
> + * If all optional features are supported then the coding will step
> + * through multiple states for these combination transitions:
Maybe "The coding will step through multiple states for some combination
transitions; if all optional features are supported, this means the
following ones:"?
> + * RESUMING -> STOP -> RUNNING_P2P
> + * RESUMING -> STOP -> RUNNING_P2P -> RUNNING
> * RESUMING -> STOP -> STOP_COPY
> - * RUNNING -> STOP -> RESUMING
> - * RUNNING -> STOP -> STOP_COPY
> + * RUNNING -> RUNNING_P2P -> STOP
> + * RUNNING -> RUNNING_P2P -> STOP -> RESUMING
> + * RUNNING -> RUNNING_P2P -> STOP -> STOP_COPY
> + * RUNNING_P2P -> STOP -> RESUMING
> + * RUNNING_P2P -> STOP -> STOP_COPY
> + * STOP -> RUNNING_P2P -> RUNNING
> * STOP_COPY -> STOP -> RESUMING
> - * STOP_COPY -> STOP -> RUNNING
> + * STOP_COPY -> STOP -> RUNNING_P2P
> + * STOP_COPY -> STOP -> RUNNING_P2P -> RUNNING
> */
