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, 217 insertions, 0 deletions

diff --git a/drivers/input/serio/pcips2.c b/drivers/input/serio/pcips2.c
new file mode 100644
index 000000000..78f47b0ca
--- /dev/null
+++ b/drivers/input/serio/pcips2.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/drivers/input/serio/pcips2.c
+ *
+ *  Copyright (C) 2003 Russell King, All Rights Reserved.
+ *
+ *  I'm not sure if this is a generic PS/2 PCI interface or specific to
+ *  the Mobility Electronics docking station.
+ */
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/input.h>
+#include <linux/pci.h>
+#include <linux/slab.h>
+#include <linux/serio.h>
+#include <linux/delay.h>
+#include <asm/io.h>
+
+#define PS2_CTRL		(0)
+#define PS2_STATUS		(1)
+#define PS2_DATA		(2)
+
+#define PS2_CTRL_CLK		(1<<0)
+#define PS2_CTRL_DAT		(1<<1)
+#define PS2_CTRL_TXIRQ		(1<<2)
+#define PS2_CTRL_ENABLE		(1<<3)
+#define PS2_CTRL_RXIRQ		(1<<4)
+
+#define PS2_STAT_CLK		(1<<0)
+#define PS2_STAT_DAT		(1<<1)
+#define PS2_STAT_PARITY		(1<<2)
+#define PS2_STAT_RXFULL		(1<<5)
+#define PS2_STAT_TXBUSY		(1<<6)
+#define PS2_STAT_TXEMPTY	(1<<7)
+
+struct pcips2_data {
+	struct serio	*io;
+	unsigned int	base;
+	struct pci_dev	*dev;
+};
+
+static int pcips2_write(struct serio *io, unsigned char val)
+{
+	struct pcips2_data *ps2if = io->port_data;
+	unsigned int stat;
+
+	do {
+		stat = inb(ps2if->base + PS2_STATUS);
+		cpu_relax();
+	} while (!(stat & PS2_STAT_TXEMPTY));
+
+	outb(val, ps2if->base + PS2_DATA);
+
+	return 0;
+}
+
+static irqreturn_t pcips2_interrupt(int irq, void *devid)
+{
+	struct pcips2_data *ps2if = devid;
+	unsigned char status, scancode;
+	int handled = 0;
+
+	do {
+		unsigned int flag;
+
+		status = inb(ps2if->base + PS2_STATUS);
+		if (!(status & PS2_STAT_RXFULL))
+			break;
+		handled = 1;
+		scancode = inb(ps2if->base + PS2_DATA);
+		if (status == 0xff && scancode == 0xff)
+			break;
+
+		flag = (status & PS2_STAT_PARITY) ? 0 : SERIO_PARITY;
+
+		if (hweight8(scancode) & 1)
+			flag ^= SERIO_PARITY;
+
+		serio_interrupt(ps2if->io, scancode, flag);
+	} while (1);
+	return IRQ_RETVAL(handled);
+}
+
+static void pcips2_flush_input(struct pcips2_data *ps2if)
+{
+	unsigned char status, scancode;
+
+	do {
+		status = inb(ps2if->base + PS2_STATUS);
+		if (!(status & PS2_STAT_RXFULL))
+			break;
+		scancode = inb(ps2if->base + PS2_DATA);
+		if (status == 0xff && scancode == 0xff)
+			break;
+	} while (1);
+}
+
+static int pcips2_open(struct serio *io)
+{
+	struct pcips2_data *ps2if = io->port_data;
+	int ret, val = 0;
+
+	outb(PS2_CTRL_ENABLE, ps2if->base);
+	pcips2_flush_input(ps2if);
+
+	ret = request_irq(ps2if->dev->irq, pcips2_interrupt, IRQF_SHARED,
+			  "pcips2", ps2if);
+	if (ret == 0)
+		val = PS2_CTRL_ENABLE | PS2_CTRL_RXIRQ;
+
+	outb(val, ps2if->base);
+
+	return ret;
+}
+
+static void pcips2_close(struct serio *io)
+{
+	struct pcips2_data *ps2if = io->port_data;
+
+	outb(0, ps2if->base);
+
+	free_irq(ps2if->dev->irq, ps2if);
+}
+
+static int pcips2_probe(struct pci_dev *dev, const struct pci_device_id *id)
+{
+	struct pcips2_data *ps2if;
+	struct serio *serio;
+	int ret;
+
+	ret = pci_enable_device(dev);
+	if (ret)
+		goto out;
+
+	ret = pci_request_regions(dev, "pcips2");
+	if (ret)
+		goto disable;
+
+	ps2if = kzalloc_obj(*ps2if);
+	serio = kzalloc_obj(*serio);
+	if (!ps2if || !serio) {
+		ret = -ENOMEM;
+		goto release;
+	}
+
+
+	serio->id.type		= SERIO_8042;
+	serio->write		= pcips2_write;
+	serio->open		= pcips2_open;
+	serio->close		= pcips2_close;
+	strscpy(serio->name, pci_name(dev), sizeof(serio->name));
+	strscpy(serio->phys, dev_name(&dev->dev), sizeof(serio->phys));
+	serio->port_data	= ps2if;
+	serio->dev.parent	= &dev->dev;
+	ps2if->io		= serio;
+	ps2if->dev		= dev;
+	ps2if->base		= pci_resource_start(dev, 0);
+
+	pci_set_drvdata(dev, ps2if);
+
+	serio_register_port(ps2if->io);
+	return 0;
+
+ release:
+	kfree(ps2if);
+	kfree(serio);
+	pci_release_regions(dev);
+ disable:
+	pci_disable_device(dev);
+ out:
+	return ret;
+}
+
+static void pcips2_remove(struct pci_dev *dev)
+{
+	struct pcips2_data *ps2if = pci_get_drvdata(dev);
+
+	serio_unregister_port(ps2if->io);
+	kfree(ps2if);
+	pci_release_regions(dev);
+	pci_disable_device(dev);
+}
+
+static const struct pci_device_id pcips2_ids[] = {
+	{
+		.vendor		= 0x14f2,	/* MOBILITY */
+		.device		= 0x0123,	/* Keyboard */
+		.subvendor	= PCI_ANY_ID,
+		.subdevice	= PCI_ANY_ID,
+		.class		= PCI_CLASS_INPUT_KEYBOARD << 8,
+		.class_mask	= 0xffff00,
+	},
+	{
+		.vendor		= 0x14f2,	/* MOBILITY */
+		.device		= 0x0124,	/* Mouse */
+		.subvendor	= PCI_ANY_ID,
+		.subdevice	= PCI_ANY_ID,
+		.class		= PCI_CLASS_INPUT_MOUSE << 8,
+		.class_mask	= 0xffff00,
+	},
+	{ 0, }
+};
+MODULE_DEVICE_TABLE(pci, pcips2_ids);
+
+static struct pci_driver pcips2_driver = {
+	.name			= "pcips2",
+	.id_table		= pcips2_ids,
+	.probe			= pcips2_probe,
+	.remove			= pcips2_remove,
+};
+
+module_pci_driver(pcips2_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Russell King <rmk@arm.linux.org.uk>");
+MODULE_DESCRIPTION("PCI PS/2 keyboard/mouse driver");