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, 49 insertions, 0 deletions

diff --git a/include/sound/sof/xtensa.h b/include/sound/sof/xtensa.h
new file mode 100644
index 000000000..ef70f8e26
--- /dev/null
+++ b/include/sound/sof/xtensa.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause) */
+/*
+ * This file is provided under a dual BSD/GPLv2 license.  When using or
+ * redistributing this file, you may do so under either license.
+ *
+ * Copyright(c) 2018 Intel Corporation
+ */
+
+#ifndef __INCLUDE_SOUND_SOF_XTENSA_H__
+#define __INCLUDE_SOUND_SOF_XTENSA_H__
+
+#include <sound/sof/header.h>
+
+/*
+ * Architecture specific debug
+ */
+
+/* Xtensa Firmware Oops data */
+struct sof_ipc_dsp_oops_xtensa {
+	struct sof_ipc_dsp_oops_arch_hdr arch_hdr;
+	struct sof_ipc_dsp_oops_plat_hdr plat_hdr;
+	uint32_t exccause;
+	uint32_t excvaddr;
+	uint32_t ps;
+	uint32_t epc1;
+	uint32_t epc2;
+	uint32_t epc3;
+	uint32_t epc4;
+	uint32_t epc5;
+	uint32_t epc6;
+	uint32_t epc7;
+	uint32_t eps2;
+	uint32_t eps3;
+	uint32_t eps4;
+	uint32_t eps5;
+	uint32_t eps6;
+	uint32_t eps7;
+	uint32_t depc;
+	uint32_t intenable;
+	uint32_t interrupt;
+	uint32_t sar;
+	uint32_t debugcause;
+	uint32_t windowbase;
+	uint32_t windowstart;
+	uint32_t excsave1;
+	uint32_t ar[];
+}  __packed;
+
+#endif