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/drivers/input/mouse/maplemouse.c b/drivers/input/mouse/maplemouse.c
new file mode 100644
index 000000000..0c8f7d1b0
--- /dev/null
+++ b/drivers/input/mouse/maplemouse.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *	SEGA Dreamcast mouse driver
+ *	Based on drivers/usb/usbmouse.c
+ *
+ *	Copyright (c) Yaegashi Takeshi, 2001
+ *	Copyright (c) Adrian McMenamin, 2008 - 2009
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/timer.h>
+#include <linux/maple.h>
+
+MODULE_AUTHOR("Adrian McMenamin <adrian@mcmen.demon.co.uk>");
+MODULE_DESCRIPTION("SEGA Dreamcast mouse driver");
+MODULE_LICENSE("GPL");
+
+struct dc_mouse {
+	struct input_dev *dev;
+	struct maple_device *mdev;
+};
+
+static void dc_mouse_callback(struct mapleq *mq)
+{
+	int buttons, relx, rely, relz;
+	struct maple_device *mapledev = mq->dev;
+	struct dc_mouse *mse = maple_get_drvdata(mapledev);
+	struct input_dev *dev = mse->dev;
+	unsigned char *res = mq->recvbuf->buf;
+
+	buttons = ~res[8];
+	relx = *(unsigned short *)(res + 12) - 512;
+	rely = *(unsigned short *)(res + 14) - 512;
+	relz = *(unsigned short *)(res + 16) - 512;
+
+	input_report_key(dev, BTN_LEFT,   buttons & 4);
+	input_report_key(dev, BTN_MIDDLE, buttons & 9);
+	input_report_key(dev, BTN_RIGHT,  buttons & 2);
+	input_report_rel(dev, REL_X,      relx);
+	input_report_rel(dev, REL_Y,      rely);
+	input_report_rel(dev, REL_WHEEL,  relz);
+	input_sync(dev);
+}
+
+static int dc_mouse_open(struct input_dev *dev)
+{
+	struct dc_mouse *mse = input_get_drvdata(dev);
+
+	maple_getcond_callback(mse->mdev, dc_mouse_callback, HZ/50,
+		MAPLE_FUNC_MOUSE);
+
+	return 0;
+}
+
+static void dc_mouse_close(struct input_dev *dev)
+{
+	struct dc_mouse *mse = input_get_drvdata(dev);
+
+	maple_getcond_callback(mse->mdev, dc_mouse_callback, 0,
+		MAPLE_FUNC_MOUSE);
+}
+
+/* allow the mouse to be used */
+static int probe_maple_mouse(struct device *dev)
+{
+	struct maple_device *mdev = to_maple_dev(dev);
+	struct maple_driver *mdrv = to_maple_driver(dev->driver);
+	int error;
+	struct input_dev *input_dev;
+	struct dc_mouse *mse;
+
+	mse = kzalloc_obj(*mse);
+	if (!mse) {
+		error = -ENOMEM;
+		goto fail;
+	}
+
+	input_dev = input_allocate_device();
+	if (!input_dev) {
+		error = -ENOMEM;
+		goto fail_nomem;
+	}
+
+	mse->dev = input_dev;
+	mse->mdev = mdev;
+
+	maple_set_drvdata(mdev, mse);
+
+	input_set_drvdata(input_dev, mse);
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
+	input_dev->keybit[BIT_WORD(BTN_MOUSE)] = BIT_MASK(BTN_LEFT) |
+		BIT_MASK(BTN_RIGHT) | BIT_MASK(BTN_MIDDLE);
+	input_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y) |
+		BIT_MASK(REL_WHEEL);
+	input_dev->open = dc_mouse_open;
+	input_dev->close = dc_mouse_close;
+	input_dev->name = mdev->product_name;
+	input_dev->id.bustype = BUS_HOST;
+	error =	input_register_device(input_dev);
+	if (error)
+		goto fail_register;
+
+	mdev->driver = mdrv;
+
+	return error;
+
+fail_register:
+	input_free_device(input_dev);
+	maple_set_drvdata(mdev, NULL);
+fail_nomem:
+	kfree(mse);
+fail:
+	return error;
+}
+
+static int remove_maple_mouse(struct device *dev)
+{
+	struct maple_device *mdev = to_maple_dev(dev);
+	struct dc_mouse *mse = maple_get_drvdata(mdev);
+
+	mdev->callback = NULL;
+	input_unregister_device(mse->dev);
+	maple_set_drvdata(mdev, NULL);
+	kfree(mse);
+
+	return 0;
+}
+
+static struct maple_driver dc_mouse_driver = {
+	.function =	MAPLE_FUNC_MOUSE,
+	.drv = {
+		.name = "Dreamcast_mouse",
+		.probe = probe_maple_mouse,
+		.remove = remove_maple_mouse,
+	},
+};
+
+static int __init dc_mouse_init(void)
+{
+	return maple_driver_register(&dc_mouse_driver);
+}
+
+static void __exit dc_mouse_exit(void)
+{
+	maple_driver_unregister(&dc_mouse_driver);
+}
+
+module_init(dc_mouse_init);
+module_exit(dc_mouse_exit);