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, 220 insertions, 0 deletions

diff --git a/drivers/char/uv_mmtimer.c b/drivers/char/uv_mmtimer.c
new file mode 100644
index 000000000..956ebe208
--- /dev/null
+++ b/drivers/char/uv_mmtimer.c
@@ -0,0 +1,220 @@
+/*
+ * Timer device implementation for SGI UV platform.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (c) 2009 Silicon Graphics, Inc.  All rights reserved.
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/ioctl.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/mmtimer.h>
+#include <linux/miscdevice.h>
+#include <linux/posix-timers.h>
+#include <linux/interrupt.h>
+#include <linux/time.h>
+#include <linux/math64.h>
+
+#include <asm/genapic.h>
+#include <asm/uv/uv_hub.h>
+#include <asm/uv/bios.h>
+#include <asm/uv/uv.h>
+
+MODULE_AUTHOR("Dimitri Sivanich <sivanich@sgi.com>");
+MODULE_DESCRIPTION("SGI UV Memory Mapped RTC Timer");
+MODULE_LICENSE("GPL");
+
+/* name of the device, usually in /dev */
+#define UV_MMTIMER_NAME "mmtimer"
+#define UV_MMTIMER_DESC "SGI UV Memory Mapped RTC Timer"
+#define UV_MMTIMER_VERSION "1.0"
+
+static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
+						unsigned long arg);
+static int uv_mmtimer_mmap(struct file *file, struct vm_area_struct *vma);
+
+/*
+ * Period in femtoseconds (10^-15 s)
+ */
+static unsigned long uv_mmtimer_femtoperiod;
+
+static const struct file_operations uv_mmtimer_fops = {
+	.owner = THIS_MODULE,
+	.mmap =	uv_mmtimer_mmap,
+	.unlocked_ioctl = uv_mmtimer_ioctl,
+	.llseek = noop_llseek,
+};
+
+/**
+ * uv_mmtimer_ioctl - ioctl interface for /dev/uv_mmtimer
+ * @file: file structure for the device
+ * @cmd: command to execute
+ * @arg: optional argument to command
+ *
+ * Executes the command specified by @cmd.  Returns 0 for success, < 0 for
+ * failure.
+ *
+ * Valid commands:
+ *
+ * %MMTIMER_GETOFFSET - Should return the offset (relative to the start
+ * of the page where the registers are mapped) for the counter in question.
+ *
+ * %MMTIMER_GETRES - Returns the resolution of the clock in femto (10^-15)
+ * seconds
+ *
+ * %MMTIMER_GETFREQ - Copies the frequency of the clock in Hz to the address
+ * specified by @arg
+ *
+ * %MMTIMER_GETBITS - Returns the number of bits in the clock's counter
+ *
+ * %MMTIMER_MMAPAVAIL - Returns 1 if registers can be mmap'd into userspace
+ *
+ * %MMTIMER_GETCOUNTER - Gets the current value in the counter and places it
+ * in the address specified by @arg.
+ */
+static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
+						unsigned long arg)
+{
+	int ret = 0;
+
+	switch (cmd) {
+	case MMTIMER_GETOFFSET:	/* offset of the counter */
+		/*
+		 * Starting with HUB rev 2.0, the UV RTC register is
+		 * replicated across all cachelines of it's own page.
+		 * This allows faster simultaneous reads from a given socket.
+		 *
+		 * The offset returned is in 64 bit units.
+		 */
+		if (uv_get_min_hub_revision_id() == 1)
+			ret = 0;
+		else
+			ret = ((uv_blade_processor_id() * L1_CACHE_BYTES) %
+					PAGE_SIZE) / 8;
+		break;
+
+	case MMTIMER_GETRES: /* resolution of the clock in 10^-15 s */
+		if (copy_to_user((unsigned long __user *)arg,
+				&uv_mmtimer_femtoperiod, sizeof(unsigned long)))
+			ret = -EFAULT;
+		break;
+
+	case MMTIMER_GETFREQ: /* frequency in Hz */
+		if (copy_to_user((unsigned long __user *)arg,
+				&sn_rtc_cycles_per_second,
+				sizeof(unsigned long)))
+			ret = -EFAULT;
+		break;
+
+	case MMTIMER_GETBITS: /* number of bits in the clock */
+		ret = hweight64(UVH_RTC_REAL_TIME_CLOCK_MASK);
+		break;
+
+	case MMTIMER_MMAPAVAIL:
+		ret = 1;
+		break;
+
+	case MMTIMER_GETCOUNTER:
+		if (copy_to_user((unsigned long __user *)arg,
+				(unsigned long *)uv_local_mmr_address(UVH_RTC),
+				sizeof(unsigned long)))
+			ret = -EFAULT;
+		break;
+	default:
+		ret = -ENOTTY;
+		break;
+	}
+	return ret;
+}
+
+/**
+ * uv_mmtimer_mmap - maps the clock's registers into userspace
+ * @file: file structure for the device
+ * @vma: VMA to map the registers into
+ *
+ * Calls remap_pfn_range() to map the clock's registers into
+ * the calling process' address space.
+ */
+static int uv_mmtimer_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	unsigned long uv_mmtimer_addr;
+
+	if (vma->vm_end - vma->vm_start != PAGE_SIZE)
+		return -EINVAL;
+
+	if (vma->vm_flags & VM_WRITE)
+		return -EPERM;
+
+	if (PAGE_SIZE > (1 << 16))
+		return -ENOSYS;
+
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+	uv_mmtimer_addr = UV_LOCAL_MMR_BASE | UVH_RTC;
+	uv_mmtimer_addr &= ~(PAGE_SIZE - 1);
+	uv_mmtimer_addr &= 0xfffffffffffffffUL;
+
+	if (remap_pfn_range(vma, vma->vm_start, uv_mmtimer_addr >> PAGE_SHIFT,
+					PAGE_SIZE, vma->vm_page_prot)) {
+		printk(KERN_ERR "remap_pfn_range failed in uv_mmtimer_mmap\n");
+		return -EAGAIN;
+	}
+
+	return 0;
+}
+
+static struct miscdevice uv_mmtimer_miscdev = {
+	MISC_DYNAMIC_MINOR,
+	UV_MMTIMER_NAME,
+	&uv_mmtimer_fops
+};
+
+
+/**
+ * uv_mmtimer_init - device initialization routine
+ *
+ * Does initial setup for the uv_mmtimer device.
+ */
+static int __init uv_mmtimer_init(void)
+{
+	if (!is_uv_system()) {
+		printk(KERN_ERR "%s: Hardware unsupported\n", UV_MMTIMER_NAME);
+		return -1;
+	}
+
+	/*
+	 * Sanity check the cycles/sec variable
+	 */
+	if (sn_rtc_cycles_per_second < 100000) {
+		printk(KERN_ERR "%s: unable to determine clock frequency\n",
+		       UV_MMTIMER_NAME);
+		return -1;
+	}
+
+	uv_mmtimer_femtoperiod = ((unsigned long)1E15 +
+				sn_rtc_cycles_per_second / 2) /
+				sn_rtc_cycles_per_second;
+
+	if (misc_register(&uv_mmtimer_miscdev)) {
+		printk(KERN_ERR "%s: failed to register device\n",
+		       UV_MMTIMER_NAME);
+		return -1;
+	}
+
+	printk(KERN_INFO "%s: v%s, %ld MHz\n", UV_MMTIMER_DESC,
+		UV_MMTIMER_VERSION,
+		sn_rtc_cycles_per_second/(unsigned long)1E6);
+
+	return 0;
+}
+
+module_init(uv_mmtimer_init);