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, 139 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ps3.c b/arch/powerpc/boot/ps3.c
new file mode 100644
index 000000000..89ff46b8b
--- /dev/null
+++ b/arch/powerpc/boot/ps3.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  PS3 bootwrapper support.
+ *
+ *  Copyright (C) 2007 Sony Computer Entertainment Inc.
+ *  Copyright 2007 Sony Corp.
+ */
+
+#include <stdarg.h>
+#include <stddef.h>
+#include "types.h"
+#include "elf.h"
+#include "string.h"
+#include "stdio.h"
+#include "page.h"
+#include "ops.h"
+
+extern int lv1_panic(u64 in_1);
+extern int lv1_get_logical_partition_id(u64 *out_1);
+extern int lv1_get_logical_ppe_id(u64 *out_1);
+extern int lv1_get_repository_node_value(u64 in_1, u64 in_2, u64 in_3,
+	u64 in_4, u64 in_5, u64 *out_1, u64 *out_2);
+
+BSS_STACK(4096);
+
+/* A buffer that may be edited by tools operating on a zImage binary so as to
+ * edit the command line passed to vmlinux (by setting /chosen/bootargs).
+ * The buffer is put in its own section so that tools may locate it easier.
+ */
+
+static char cmdline[BOOT_COMMAND_LINE_SIZE]
+	__attribute__((__section__("__builtin_cmdline")));
+
+static void prep_cmdline(void *chosen)
+{
+	if (cmdline[0] == '\0')
+		getprop(chosen, "bootargs", cmdline, BOOT_COMMAND_LINE_SIZE-1);
+	else
+		setprop_str(chosen, "bootargs", cmdline);
+
+	printf("cmdline: '%s'\n", cmdline);
+}
+
+static void ps3_console_write(const char *buf, int len)
+{
+}
+
+static void ps3_exit(void)
+{
+	printf("ps3_exit\n");
+
+	/* lv1_panic will shutdown the lpar. */
+
+	lv1_panic(0); /* zero = do not reboot */
+	while (1);
+}
+
+static int ps3_repository_read_rm_size(u64 *rm_size)
+{
+	int result;
+	u64 lpar_id;
+	u64 ppe_id;
+	u64 v2;
+
+	result = lv1_get_logical_partition_id(&lpar_id);
+
+	if (result)
+		return -1;
+
+	result = lv1_get_logical_ppe_id(&ppe_id);
+
+	if (result)
+		return -1;
+
+	/*
+	 * n1: 0000000062690000 : ....bi..
+	 * n2: 7075000000000000 : pu......
+	 * n3: 0000000000000001 : ........
+	 * n4: 726d5f73697a6500 : rm_size.
+	*/
+
+	result = lv1_get_repository_node_value(lpar_id, 0x0000000062690000ULL,
+		0x7075000000000000ULL, ppe_id, 0x726d5f73697a6500ULL, rm_size,
+		&v2);
+
+	printf("%s:%d: ppe_id  %lu \n", __func__, __LINE__,
+		(unsigned long)ppe_id);
+	printf("%s:%d: lpar_id %lu \n", __func__, __LINE__,
+		(unsigned long)lpar_id);
+	printf("%s:%d: rm_size %llxh \n", __func__, __LINE__, *rm_size);
+
+	return result ? -1 : 0;
+}
+
+void ps3_copy_vectors(void)
+{
+	extern char __system_reset_kernel[];
+
+	memcpy((void *)0x100, __system_reset_kernel, 512);
+	flush_cache((void *)0x100, 512);
+}
+
+void platform_init(void)
+{
+	const u32 heapsize = 0x1000000 - (u32)_end; /* 16MiB */
+	void *chosen;
+	unsigned long ft_addr;
+	u64 rm_size;
+
+	console_ops.write = ps3_console_write;
+	platform_ops.exit = ps3_exit;
+
+	printf("\n-- PS3 bootwrapper --\n");
+
+	simple_alloc_init(_end, heapsize, 32, 64);
+	fdt_init(_dtb_start);
+
+	chosen = finddevice("/chosen");
+
+	ps3_repository_read_rm_size(&rm_size);
+	dt_fixup_memory(0, rm_size);
+
+	if (&_initrd_end > &_initrd_start) {
+		setprop_val(chosen, "linux,initrd-start", (u32)(_initrd_start));
+		setprop_val(chosen, "linux,initrd-end", (u32)(_initrd_end));
+	}
+
+	prep_cmdline(chosen);
+
+	ft_addr = dt_ops.finalize();
+
+	ps3_copy_vectors();
+
+	printf(" flat tree at 0x%lx\n\r", ft_addr);
+
+	((kernel_entry_t)0)(ft_addr, 0, NULL);
+
+	ps3_exit();
+}