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, 153 insertions, 0 deletions

diff --git a/arch/powerpc/boot/serial.c b/arch/powerpc/boot/serial.c
new file mode 100644
index 000000000..c6d32a8c3
--- /dev/null
+++ b/arch/powerpc/boot/serial.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic serial console support
+ *
+ * Author: Mark A. Greer <mgreer@mvista.com>
+ *
+ * Code in serial_edit_cmdline() copied from <file:arch/ppc/boot/simple/misc.c>
+ * and was written by Matt Porter <mporter@kernel.crashing.org>.
+ *
+ * 2001,2006 (c) MontaVista Software, Inc.
+ */
+#include <stdarg.h>
+#include <stddef.h>
+#include "types.h"
+#include "string.h"
+#include "stdio.h"
+#include "io.h"
+#include "ops.h"
+
+static int serial_open(void)
+{
+	struct serial_console_data *scdp = console_ops.data;
+	return scdp->open();
+}
+
+static void serial_write(const char *buf, int len)
+{
+	struct serial_console_data *scdp = console_ops.data;
+
+	while (*buf != '\0')
+		scdp->putc(*buf++);
+}
+
+static void serial_edit_cmdline(char *buf, int len, unsigned int timeout)
+{
+	int timer = 0, count;
+	char ch, *cp;
+	struct serial_console_data *scdp = console_ops.data;
+
+	cp = buf;
+	count = strlen(buf);
+	cp = &buf[count];
+	count++;
+
+	do {
+		if (scdp->tstc()) {
+			while (((ch = scdp->getc()) != '\n') && (ch != '\r')) {
+				/* Test for backspace/delete */
+				if ((ch == '\b') || (ch == '\177')) {
+					if (cp != buf) {
+						cp--;
+						count--;
+						printf("\b \b");
+					}
+				/* Test for ^x/^u (and wipe the line) */
+				} else if ((ch == '\030') || (ch == '\025')) {
+					while (cp != buf) {
+						cp--;
+						count--;
+						printf("\b \b");
+					}
+				} else if (count < len) {
+						*cp++ = ch;
+						count++;
+						scdp->putc(ch);
+				}
+			}
+			break;  /* Exit 'timer' loop */
+		}
+		udelay(1000);  /* 1 msec */
+	} while (timer++ < timeout);
+	*cp = 0;
+}
+
+static void serial_close(void)
+{
+	struct serial_console_data *scdp = console_ops.data;
+
+	if (scdp->close)
+		scdp->close();
+}
+
+static void *serial_get_stdout_devp(void)
+{
+	void *devp;
+	char devtype[MAX_PROP_LEN];
+	char path[MAX_PATH_LEN];
+
+	devp = finddevice("/chosen");
+	if (devp == NULL)
+		goto err_out;
+
+	if (getprop(devp, "linux,stdout-path", path, MAX_PATH_LEN) > 0 ||
+		getprop(devp, "stdout-path", path, MAX_PATH_LEN) > 0) {
+		devp = finddevice(path);
+		if (devp == NULL)
+			goto err_out;
+
+		if ((getprop(devp, "device_type", devtype, sizeof(devtype)) > 0)
+				&& !strcmp(devtype, "serial"))
+			return devp;
+	}
+err_out:
+	return NULL;
+}
+
+static struct serial_console_data serial_cd;
+
+/* Node's "compatible" property determines which serial driver to use */
+int serial_console_init(void)
+{
+	void *devp;
+	int rc = -1;
+
+	devp = serial_get_stdout_devp();
+	if (devp == NULL)
+		goto err_out;
+
+	if (dt_is_compatible(devp, "ns16550") ||
+	    dt_is_compatible(devp, "pnpPNP,501"))
+		rc = ns16550_console_init(devp, &serial_cd);
+#ifdef CONFIG_CPM
+	else if (dt_is_compatible(devp, "fsl,cpm1-scc-uart") ||
+	         dt_is_compatible(devp, "fsl,cpm1-smc-uart") ||
+	         dt_is_compatible(devp, "fsl,cpm2-scc-uart") ||
+	         dt_is_compatible(devp, "fsl,cpm2-smc-uart"))
+		rc = cpm_console_init(devp, &serial_cd);
+#endif
+#ifdef CONFIG_PPC_MPC52xx
+	else if (dt_is_compatible(devp, "fsl,mpc5200-psc-uart"))
+		rc = mpc5200_psc_console_init(devp, &serial_cd);
+#endif
+#ifdef CONFIG_PPC_POWERNV
+	else if (dt_is_compatible(devp, "ibm,opal-console-raw"))
+		rc = opal_console_init(devp, &serial_cd);
+#endif
+
+	/* Add other serial console driver calls here */
+
+	if (!rc) {
+		console_ops.open = serial_open;
+		console_ops.write = serial_write;
+		console_ops.close = serial_close;
+		console_ops.data = &serial_cd;
+
+		if (serial_cd.getc)
+			console_ops.edit_cmdline = serial_edit_cmdline;
+
+		return 0;
+	}
+err_out:
+	return -1;
+}