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Date: Tue, 1 Feb 2022 11:31:44 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Yishai Hadas <yishaih@...dia.com>
Cc: <bhelgaas@...gle.com>, <jgg@...dia.com>, <saeedm@...dia.com>,
<linux-pci@...r.kernel.org>, <kvm@...r.kernel.org>,
<netdev@...r.kernel.org>, <kuba@...nel.org>, <leonro@...dia.com>,
<kwankhede@...dia.com>, <mgurtovoy@...dia.com>, <maorg@...dia.com>
Subject: Re: [PATCH V6 mlx5-next 09/15] vfio: Extend the device migration
protocol with RUNNING_P2P
On Sun, 30 Jan 2022 18:08:20 +0200
Yishai Hadas <yishaih@...dia.com> wrote:
> From: Jason Gunthorpe <jgg@...dia.com>
>
> 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 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. 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@...dia.com>
> Signed-off-by: Yishai Hadas <yishaih@...dia.com>
> ---
> drivers/vfio/vfio.c | 70 ++++++++++++++++++++++++++++++---------
> include/linux/vfio.h | 2 ++
> include/uapi/linux/vfio.h | 34 +++++++++++++++++--
> 3 files changed, 88 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index b12be212d048..a722a1a8a48a 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1573,39 +1573,55 @@ u32 vfio_mig_get_next_state(struct vfio_device *device,
> enum vfio_device_mig_state cur_fsm,
> enum vfio_device_mig_state new_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:
> * 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:
> + * 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
> */
> static const u8 vfio_from_fsm_table[VFIO_DEVICE_NUM_STATES][VFIO_DEVICE_NUM_STATES] = {
> [VFIO_DEVICE_STATE_STOP] = {
> [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP,
> - [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING,
> + [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING_P2P,
> [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP_COPY,
> [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RESUMING,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P,
> [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> },
> [VFIO_DEVICE_STATE_RUNNING] = {
> - [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_RUNNING_P2P,
> [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING,
> - [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP,
> - [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_RUNNING_P2P,
> + [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RUNNING_P2P,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P,
> [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> },
> [VFIO_DEVICE_STATE_STOP_COPY] = {
> @@ -1613,6 +1629,7 @@ u32 vfio_mig_get_next_state(struct vfio_device *device,
> [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_STOP,
> [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP_COPY,
> [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_STOP,
> [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> },
> [VFIO_DEVICE_STATE_RESUMING] = {
> @@ -1620,6 +1637,15 @@ u32 vfio_mig_get_next_state(struct vfio_device *device,
> [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_STOP,
> [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP,
> [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RESUMING,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> + },
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = {
> + [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING,
> + [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_STOP,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P,
> [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> },
> [VFIO_DEVICE_STATE_ERROR] = {
> @@ -1627,14 +1653,26 @@ u32 vfio_mig_get_next_state(struct vfio_device *device,
> [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_ERROR,
> [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_ERROR,
> [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_ERROR,
> + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_ERROR,
> [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR,
> },
> };
> + bool have_p2p = device->migration_flags & VFIO_MIGRATION_P2P;
> +
> if (cur_fsm >= ARRAY_SIZE(vfio_from_fsm_table) ||
> new_fsm >= ARRAY_SIZE(vfio_from_fsm_table))
> return VFIO_DEVICE_STATE_ERROR;
>
> - return vfio_from_fsm_table[cur_fsm][new_fsm];
> + if (!have_p2p && (new_fsm == VFIO_DEVICE_STATE_RUNNING_P2P ||
> + cur_fsm == VFIO_DEVICE_STATE_RUNNING_P2P))
> + return VFIO_DEVICE_STATE_ERROR;
new_fsm is provided by the user, we pass set_state.device_state
directly to .migration_set_state. We should do bounds checking and
compatibility testing on the end state in the core so that we can
return an appropriate -EINVAL and -ENOSUPP respectively, otherwise
we're giving userspace a path to put the device into ERROR state, which
we claim is not allowed.
Testing cur_fsm is more an internal consistency check, maybe those
should be WARN_ON.
> +
> + cur_fsm = vfio_from_fsm_table[cur_fsm][new_fsm];
> + if (!have_p2p) {
> + while (cur_fsm == VFIO_DEVICE_STATE_RUNNING_P2P)
> + cur_fsm = vfio_from_fsm_table[cur_fsm][new_fsm];
> + }
Perhaps this could be generalized with something like:
static const unsigned int state_flags_table[VFIO_DEVICE_NUM_STATES] = {
[VFIO_DEVICE_STATE_STOP] = VFIO_MIGRATION_STOP_COPY,
[VFIO_DEVICE_STATE_RUNNING] = VFIO_MIGRATION_STOP_COPY,
[VFIO_DEVICE_STATE_STOP_COPY] = VFIO_MIGRATION_STOP_COPY,
[VFIO_DEVICE_STATE_RESUMING] = VFIO_MIGRATION_STOP_COPY,
[VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_MIGRATION_P2P,
[VFIO_DEVICE_STATE_ERROR] = ~0U,
};
while (!(state_flags_table[cur_fsm] & device->migration_flags))
cur_fsm = vfio_from_fsm_table[cur_fsm][new_fsm];
Thanks,
Alex
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