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, 288 insertions, 0 deletions

diff --git a/drivers/dio/dio.c b/drivers/dio/dio.c
new file mode 100644
index 000000000..7722d9eae
--- /dev/null
+++ b/drivers/dio/dio.c
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Code to support devices on the DIO and DIO-II bus
+ * Copyright (C) 05/1998 Peter Maydell <pmaydell@chiark.greenend.org.uk>
+ * Copyright (C) 2004 Jochen Friedrich <jochen@scram.de>
+ *
+ * This code has basically these routines at the moment:
+ * int dio_find(u_int deviceid)
+ *    Search the list of DIO devices and return the select code
+ *    of the next unconfigured device found that matches the given device ID.
+ *    Note that the deviceid parameter should be the encoded ID.
+ *    This means that framebuffers should pass it as
+ *    DIO_ENCODE_ID(DIO_ID_FBUFFER,DIO_ID2_TOPCAT)
+ *    (or whatever); everybody else just uses DIO_ID_FOOBAR.
+ * unsigned long dio_scodetophysaddr(int scode)
+ *    Return the physical address corresponding to the given select code.
+ * int dio_scodetoipl(int scode)
+ *    Every DIO card has a fixed interrupt priority level. This function
+ *    returns it, whatever it is.
+ * const char *dio_scodetoname(int scode)
+ *    Return a character string describing this board [might be "" if
+ *    not CONFIG_DIO_CONSTANTS]
+ * void dio_config_board(int scode)     mark board as configured in the list
+ * void dio_unconfig_board(int scode)   mark board as no longer configured
+ *
+ * This file is based on the way the Amiga port handles Zorro II cards,
+ * although we aren't so complicated...
+ */
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/dio.h>
+#include <linux/slab.h>                         /* kmalloc() */
+#include <linux/uaccess.h>
+#include <linux/io.h>                           /* readb() */
+
+struct dio_bus dio_bus = {
+	.resources = {
+		/* DIO range */
+		{ .name = "DIO mem", .start = 0x00600000, .end = 0x007fffff },
+		/* DIO-II range */
+		{ .name = "DIO-II mem", .start = 0x01000000, .end = 0x1fffffff }
+	},
+	.name = "DIO bus"
+};
+
+/* not a real config option yet! */
+#define CONFIG_DIO_CONSTANTS
+
+#ifdef CONFIG_DIO_CONSTANTS
+/* We associate each numeric ID with an appropriate descriptive string
+ * using a constant array of these structs.
+ * FIXME: we should be able to arrange to throw away most of the strings
+ * using the initdata stuff. Then we wouldn't need to worry about
+ * carrying them around...
+ * I think we do this by copying them into newly kmalloc()ed memory and
+ * marking the names[] array as .initdata ?
+ */
+struct dioname {
+	int id;
+	const char *name;
+};
+
+/* useful macro */
+#define DIONAME(x) { DIO_ID_##x, DIO_DESC_##x }
+#define DIOFBNAME(x) { DIO_ENCODE_ID(DIO_ID_FBUFFER, DIO_ID2_##x), DIO_DESC2_##x }
+
+static struct dioname names[] = {
+	DIONAME(DCA0), DIONAME(DCA0REM), DIONAME(DCA1), DIONAME(DCA1REM),
+	DIONAME(DCM), DIONAME(DCMREM),
+	DIONAME(LAN),
+	DIONAME(FHPIB), DIONAME(NHPIB),
+	DIONAME(SCSI0), DIONAME(SCSI1), DIONAME(SCSI2), DIONAME(SCSI3),
+	DIONAME(FBUFFER),
+	DIONAME(PARALLEL), DIONAME(VME), DIONAME(DCL), DIONAME(DCLREM),
+	DIONAME(MISC0), DIONAME(MISC1), DIONAME(MISC2), DIONAME(MISC3),
+	DIONAME(MISC4), DIONAME(MISC5), DIONAME(MISC6), DIONAME(MISC7),
+	DIONAME(MISC8), DIONAME(MISC9), DIONAME(MISC10), DIONAME(MISC11),
+	DIONAME(MISC12), DIONAME(MISC13),
+	DIOFBNAME(GATORBOX), DIOFBNAME(TOPCAT), DIOFBNAME(RENAISSANCE),
+	DIOFBNAME(LRCATSEYE), DIOFBNAME(HRCCATSEYE), DIOFBNAME(HRMCATSEYE),
+	DIOFBNAME(DAVINCI), DIOFBNAME(XXXCATSEYE), DIOFBNAME(HYPERION),
+	DIOFBNAME(XGENESIS), DIOFBNAME(TIGER), DIOFBNAME(YGENESIS)
+};
+
+#undef DIONAME
+#undef DIOFBNAME
+
+static const char unknowndioname[]
+	= "unknown DIO board, please email linux-m68k@lists.linux-m68k.org";
+
+static const char *dio_getname(int id)
+{
+	/* return pointer to a constant string describing the board with given ID */
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(names); i++)
+		if (names[i].id == id)
+			return names[i].name;
+
+	return unknowndioname;
+}
+
+#else
+
+static char dio_no_name[] = { 0 };
+#define dio_getname(_id)	(dio_no_name)
+
+#endif /* CONFIG_DIO_CONSTANTS */
+
+static void dio_dev_release(struct device *dev)
+{
+	struct dio_dev *ddev = container_of(dev, typeof(struct dio_dev), dev);
+	kfree(ddev);
+}
+
+int __init dio_find(int deviceid)
+{
+	/* Called to find a DIO device before the full bus scan has run.
+	 * Only used by the console driver.
+	 */
+	int scode, id;
+	u_char prid, secid, i;
+
+	for (scode = 0; scode < DIO_SCMAX; scode++) {
+		void *va;
+		unsigned long pa;
+
+		if (DIO_SCINHOLE(scode))
+			continue;
+
+		pa = dio_scodetophysaddr(scode);
+
+		if (!pa)
+			continue;
+
+		if (scode < DIOII_SCBASE)
+			va = (void *)(pa + DIO_VIRADDRBASE);
+		else
+			va = ioremap(pa, PAGE_SIZE);
+
+		if (copy_from_kernel_nofault(&i,
+				(unsigned char *)va + DIO_IDOFF, 1)) {
+			if (scode >= DIOII_SCBASE)
+				iounmap(va);
+			continue;	     /* no board present at that select code */
+		}
+
+		prid = DIO_ID(va);
+
+		if (DIO_NEEDSSECID(prid)) {
+			secid = DIO_SECID(va);
+			id = DIO_ENCODE_ID(prid, secid);
+		} else
+			id = prid;
+
+		if (id == deviceid) {
+			if (scode >= DIOII_SCBASE)
+				iounmap(va);
+			return scode;
+		}
+	}
+
+	return -1;
+}
+
+/* This is the function that scans the DIO space and works out what
+ * hardware is actually present.
+ */
+static int __init dio_init(void)
+{
+	int scode;
+	int i;
+	struct dio_dev *dev;
+	int error;
+
+	if (!MACH_IS_HP300)
+		return 0;
+
+	pr_info("Scanning for DIO devices...\n");
+
+	/* Initialize the DIO bus */
+	INIT_LIST_HEAD(&dio_bus.devices);
+	dev_set_name(&dio_bus.dev, "dio");
+	error = device_register(&dio_bus.dev);
+	if (error) {
+		pr_err("DIO: Error registering dio_bus\n");
+		return error;
+	}
+
+	/* Request all resources */
+	dio_bus.num_resources = (hp300_model == HP_320 ? 1 : 2);
+	for (i = 0; i < dio_bus.num_resources; i++)
+		request_resource(&iomem_resource, &dio_bus.resources[i]);
+
+	/* Register all devices */
+	for (scode = 0; scode < DIO_SCMAX; ++scode) {
+		u_char prid, secid = 0;	/* primary, secondary ID bytes */
+		u_char *va;
+		unsigned long pa;
+
+		if (DIO_SCINHOLE(scode))
+			continue;
+
+		pa = dio_scodetophysaddr(scode);
+
+		if (!pa)
+			continue;
+
+		if (scode < DIOII_SCBASE)
+			va = (void *)(pa + DIO_VIRADDRBASE);
+		else
+			va = ioremap(pa, PAGE_SIZE);
+
+		if (copy_from_kernel_nofault(&i,
+				(unsigned char *)va + DIO_IDOFF, 1)) {
+			if (scode >= DIOII_SCBASE)
+				iounmap(va);
+			continue;	      /* no board present at that select code */
+		}
+
+		/* Found a board, allocate it an entry in the list */
+		dev = kzalloc_obj(struct dio_dev);
+		if (!dev) {
+			if (scode >= DIOII_SCBASE)
+				iounmap(va);
+			return -ENOMEM;
+		}
+
+		dev->bus = &dio_bus;
+		dev->dev.parent = &dio_bus.dev;
+		dev->dev.bus = &dio_bus_type;
+		dev->dev.release = dio_dev_release;
+		dev->scode = scode;
+		dev->resource.start = pa;
+		dev->resource.end = pa + DIO_SIZE(scode, va);
+		dev_set_name(&dev->dev, "%02x", scode);
+
+		/* read the ID byte(s) and encode if necessary. */
+		prid = DIO_ID(va);
+
+		if (DIO_NEEDSSECID(prid)) {
+			secid = DIO_SECID(va);
+			dev->id = DIO_ENCODE_ID(prid, secid);
+		} else
+			dev->id = prid;
+
+		dev->ipl = DIO_IPL(va);
+		strscpy(dev->name, dio_getname(dev->id));
+		if (DIO_NEEDSSECID(prid))
+			pr_info("select code %3d: ipl %u: ID %02X:%02X: %s\n",
+				dev->scode, dev->ipl, prid, secid, dev->name);
+		else
+			pr_info("select code %3d: ipl %u: ID %02X: %s\n",
+				dev->scode, dev->ipl, prid, dev->name);
+
+		if (scode >= DIOII_SCBASE)
+			iounmap(va);
+		error = device_register(&dev->dev);
+		if (error) {
+			pr_err("DIO: Error registering device %s\n", dev->name);
+			put_device(&dev->dev);
+			continue;
+		}
+		error = dio_create_sysfs_dev_files(dev);
+		if (error)
+			dev_err(&dev->dev, "Error creating sysfs files\n");
+	}
+	return 0;
+}
+
+subsys_initcall(dio_init);
+
+/* Bear in mind that this is called in the very early stages of initialisation
+ * in order to get the address of the serial port for the console...
+ */
+unsigned long dio_scodetophysaddr(int scode)
+{
+	if (scode >= DIOII_SCBASE)
+		return (DIOII_BASE + (scode - 132) * DIOII_DEVSIZE);
+	else if (scode > DIO_SCMAX || scode < 0)
+		return 0;
+	else if (DIO_SCINHOLE(scode))
+		return 0;
+
+	return (DIO_BASE + scode * DIO_DEVSIZE);
+}