sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 173 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-hisi-sec b/Documentation/ABI/testing/debugfs-hisi-sec
new file mode 100644
index 000000000..676e2dc2d
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-hisi-sec
@@ -0,0 +1,173 @@
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/clear_enable
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Enabling/disabling of clear action after reading
+		the SEC debug registers.
+		0: disable, 1: enable.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/current_qm
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	One SEC controller has one PF and multiple VFs, each function
+		has a QM. This file can be used to select the QM which below
+		qm refers to.
+		Only available for PF.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/alg_qos
+Date:		Jun 2021
+Contact:	linux-crypto@vger.kernel.org
+Description:	The <bdf> is related the function for PF and VF.
+		SEC driver supports to configure each function's QoS, the driver
+		supports to write <bdf> value to alg_qos in the host. Such as
+		"echo <bdf> value > alg_qos". The qos value is 1~1000, means
+		1/1000~1000/1000 of total QoS. The driver reading alg_qos to
+		get related QoS in the host and VM, Such as "cat alg_qos".
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/dev_usage
+Date:		Mar 2026
+Contact:	linux-crypto@vger.kernel.org
+Description:	Query the real-time bandwidth usage of device.
+		Returns the bandwidth usage of each channel on the device.
+		The returned number is in percentage.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/qm_regs
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump of QM related debug registers.
+		Available for PF and VF in host. VF in guest currently only
+		has one debug register.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/current_q
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	One QM of SEC may contain multiple queues. Select specific
+		queue to show its debug registers in above 'regs'.
+		Only available for PF.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/clear_enable
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Enabling/disabling of clear action after reading
+		the SEC's QM debug registers.
+		0: disable, 1: enable.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/err_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of invalid interrupts for
+		QM task completion.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/aeq_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of QM async event queue interrupts.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/abnormal_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of interrupts for QM abnormal event.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/create_qp_err
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of queue allocation errors.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/mb_err
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of failed QM mailbox commands.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/status
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the status of the QM.
+		Two states: work, stop.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/diff_regs
+Date:		Mar 2022
+Contact:	linux-crypto@vger.kernel.org
+Description:	QM debug registers(regs) read hardware register value. This
+		node is used to show the change of the qm register values. This
+		node can be help users to check the change of register values.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/qm_state
+Date:		Jan 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the state of the device.
+		0: busy, 1: idle.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/dev_timeout
+Date:		Feb 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Set the wait time when stop queue fails. Available for both PF
+		and VF, and take no other effect on SEC.
+		0: not wait(default), others value: wait dev_timeout * 20 microsecond.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/dev_state
+Date:		Feb 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the stop queue status of the QM. The default value is 0,
+		if dev_timeout is set, when stop queue fails, the dev_state
+		will return non-zero value. Available for both PF and VF,
+		and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/diff_regs
+Date:		Mar 2022
+Contact:	linux-crypto@vger.kernel.org
+Description:	SEC debug registers(regs) read hardware register value. This
+		node is used to show the change of the register values. This
+		node can be help users to check the change of register values.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/send_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of sent requests.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/recv_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of received requests.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/send_busy_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of requests sent with returning busy.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/err_bd_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of BD type error requests
+		to be received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/invalid_req_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of invalid requests being received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/done_flag_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of completed but marked error requests
+		to be received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:           /sys/kernel/debug/hisi_sec2/<bdf>/cap_regs
+Date:           Oct 2024
+Contact:        linux-crypto@vger.kernel.org
+Description:    Dump the values of the qm and sec capability bit registers and
+                support the query of device specifications to facilitate fault locating.
+                Available for both PF and VF, and take no other effect on SEC.