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, 95 insertions, 0 deletions

diff --git a/drivers/mtd/maps/solutionengine.c b/drivers/mtd/maps/solutionengine.c
new file mode 100644
index 000000000..c07f21b20
--- /dev/null
+++ b/drivers/mtd/maps/solutionengine.c
@@ -0,0 +1,95 @@
+/*
+ * Flash and EPROM on Hitachi Solution Engine and similar boards.
+ *
+ * (C) 2001 Red Hat, Inc.
+ *
+ * GPL'd
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <asm/io.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+#include <linux/errno.h>
+
+static struct mtd_info *flash_mtd;
+static struct mtd_info *eprom_mtd;
+
+struct map_info soleng_eprom_map = {
+	.name = "Solution Engine EPROM",
+	.size = 0x400000,
+	.bankwidth = 4,
+};
+
+struct map_info soleng_flash_map = {
+	.name = "Solution Engine FLASH",
+	.size = 0x400000,
+	.bankwidth = 4,
+};
+
+static const char * const probes[] = { "RedBoot", "cmdlinepart", NULL };
+
+static int __init init_soleng_maps(void)
+{
+	/* First probe at offset 0 */
+	soleng_flash_map.phys = 0;
+	soleng_flash_map.virt = (void __iomem *)P2SEGADDR(0);
+	soleng_eprom_map.phys = 0x01000000;
+	soleng_eprom_map.virt = (void __iomem *)P1SEGADDR(0x01000000);
+	simple_map_init(&soleng_eprom_map);
+	simple_map_init(&soleng_flash_map);
+
+	printk(KERN_NOTICE "Probing for flash chips at 0x00000000:\n");
+	flash_mtd = do_map_probe("cfi_probe", &soleng_flash_map);
+	if (!flash_mtd) {
+		/* Not there. Try swapping */
+		printk(KERN_NOTICE "Probing for flash chips at 0x01000000:\n");
+		soleng_flash_map.phys = 0x01000000;
+		soleng_flash_map.virt = P2SEGADDR(0x01000000);
+		soleng_eprom_map.phys = 0;
+		soleng_eprom_map.virt = P1SEGADDR(0);
+		flash_mtd = do_map_probe("cfi_probe", &soleng_flash_map);
+		if (!flash_mtd) {
+			/* Eep. */
+			printk(KERN_NOTICE "Flash chips not detected at either possible location.\n");
+			return -ENXIO;
+		}
+	}
+	printk(KERN_NOTICE "Solution Engine: Flash at 0x%pap, EPROM at 0x%pap\n",
+	       &soleng_flash_map.phys,
+	       &soleng_eprom_map.phys);
+	flash_mtd->owner = THIS_MODULE;
+
+	eprom_mtd = do_map_probe("map_rom", &soleng_eprom_map);
+	if (eprom_mtd) {
+		eprom_mtd->owner = THIS_MODULE;
+		mtd_device_register(eprom_mtd, NULL, 0);
+	}
+
+	mtd_device_parse_register(flash_mtd, probes, NULL, NULL, 0);
+
+	return 0;
+}
+
+static void __exit cleanup_soleng_maps(void)
+{
+	if (eprom_mtd) {
+		mtd_device_unregister(eprom_mtd);
+		map_destroy(eprom_mtd);
+	}
+
+	mtd_device_unregister(flash_mtd);
+	map_destroy(flash_mtd);
+}
+
+module_init(init_soleng_maps);
+module_exit(cleanup_soleng_maps);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
+MODULE_DESCRIPTION("MTD map driver for Hitachi SolutionEngine (and similar) boards");
+