aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/vsyscall_64.c
blob: 3e682184d76c7997d090430db61d52e4826270e8 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
/*
 *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
 *  Copyright 2003 Andi Kleen, SuSE Labs.
 *
 *  Thanks to hpa@transmeta.com for some useful hint.
 *  Special thanks to Ingo Molnar for his early experience with
 *  a different vsyscall implementation for Linux/IA32 and for the name.
 *
 *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
 *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
 *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
 *  jumping out of line if necessary. We cannot add more with this
 *  mechanism because older kernels won't return -ENOSYS.
 *  If we want more than four we need a vDSO.
 *
 *  Note: the concept clashes with user mode linux. If you use UML and
 *  want per guest time just set the kernel.vsyscall64 sysctl to 0.
 */

/* Disable profiling for userspace code: */
#define DISABLE_BRANCH_PROFILING

#include <linux/time.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/seqlock.h>
#include <linux/jiffies.h>
#include <linux/sysctl.h>
#include <linux/clocksource.h>
#include <linux/getcpu.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/notifier.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/unistd.h>
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <asm/desc.h>
#include <asm/topology.h>
#include <asm/vgtod.h>

#define __vsyscall(nr) \
		__attribute__ ((unused, __section__(".vsyscall_" #nr))) notrace
#define __syscall_clobber "r11","cx","memory"

DEFINE_VVAR(int, vgetcpu_mode);
DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
{
	.lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
	.sysctl_enabled = 1,
};

void update_vsyscall_tz(void)
{
	unsigned long flags;

	write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
	/* sys_tz has changed */
	vsyscall_gtod_data.sys_tz = sys_tz;
	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}

void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
			struct clocksource *clock, u32 mult)
{
	unsigned long flags;

	write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
	/* copy vsyscall data */
	vsyscall_gtod_data.clock.vread = clock->vread;
	vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
	vsyscall_gtod_data.clock.mask = clock->mask;
	vsyscall_gtod_data.clock.mult = mult;
	vsyscall_gtod_data.clock.shift = clock->shift;
	vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
	vsyscall_gtod_data.wall_to_monotonic = *wtm;
	vsyscall_gtod_data.wall_time_coarse = __current_kernel_time();
	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}

/* RED-PEN may want to readd seq locking, but then the variable should be
 * write-once.
 */
static __always_inline void do_get_tz(struct timezone * tz)
{
	*tz = VVAR(vsyscall_gtod_data).sys_tz;
}

static __always_inline int gettimeofday(struct timeval *tv, struct timezone *tz)
{
	int ret;
	asm volatile("syscall"
		: "=a" (ret)
		: "0" (__NR_gettimeofday),"D" (tv),"S" (tz)
		: __syscall_clobber );
	return ret;
}

static __always_inline long time_syscall(long *t)
{
	long secs;
	asm volatile("syscall"
		: "=a" (secs)
		: "0" (__NR_time),"D" (t) : __syscall_clobber);
	return secs;
}

static __always_inline void do_vgettimeofday(struct timeval * tv)
{
	cycle_t now, base, mask, cycle_delta;
	unsigned seq;
	unsigned long mult, shift, nsec;
	cycle_t (*vread)(void);
	do {
		seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);

		vread = VVAR(vsyscall_gtod_data).clock.vread;
		if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled ||
			     !vread)) {
			gettimeofday(tv,NULL);
			return;
		}

		now = vread();
		base = VVAR(vsyscall_gtod_data).clock.cycle_last;
		mask = VVAR(vsyscall_gtod_data).clock.mask;
		mult = VVAR(vsyscall_gtod_data).clock.mult;
		shift = VVAR(vsyscall_gtod_data).clock.shift;

		tv->tv_sec = VVAR(vsyscall_gtod_data).wall_time_sec;
		nsec = VVAR(vsyscall_gtod_data).wall_time_nsec;
	} while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));

	/* calculate interval: */
	cycle_delta = (now - base) & mask;
	/* convert to nsecs: */
	nsec += (cycle_delta * mult) >> shift;

	while (nsec >= NSEC_PER_SEC) {
		tv->tv_sec += 1;
		nsec -= NSEC_PER_SEC;
	}
	tv->tv_usec = nsec / NSEC_PER_USEC;
}

int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
{
	if (tv)
		do_vgettimeofday(tv);
	if (tz)
		do_get_tz(tz);
	return 0;
}

/* This will break when the xtime seconds get inaccurate, but that is
 * unlikely */
time_t __vsyscall(1) vtime(time_t *t)
{
	unsigned seq;
	time_t result;
	if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
		return time_syscall(t);

	do {
		seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);

		result = VVAR(vsyscall_gtod_data).wall_time_sec;

	} while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));

	if (t)
		*t = result;
	return result;
}

/* Fast way to get current CPU and node.
   This helps to do per node and per CPU caches in user space.
   The result is not guaranteed without CPU affinity, but usually
   works out because the scheduler tries to keep a thread on the same
   CPU.

   tcache must point to a two element sized long array.
   All arguments can be NULL. */
long __vsyscall(2)
vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
{
	unsigned int p;
	unsigned long j = 0;

	/* Fast cache - only recompute value once per jiffies and avoid
	   relatively costly rdtscp/cpuid otherwise.
	   This works because the scheduler usually keeps the process
	   on the same CPU and this syscall doesn't guarantee its
	   results anyways.
	   We do this here because otherwise user space would do it on
	   its own in a likely inferior way (no access to jiffies).
	   If you don't like it pass NULL. */
	if (tcache && tcache->blob[0] == (j = VVAR(jiffies))) {
		p = tcache->blob[1];
	} else if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
		/* Load per CPU data from RDTSCP */
		native_read_tscp(&p);
	} else {
		/* Load per CPU data from GDT */
		asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
	}
	if (tcache) {
		tcache->blob[0] = j;
		tcache->blob[1] = p;
	}
	if (cpu)
		*cpu = p & 0xfff;
	if (node)
		*node = p >> 12;
	return 0;
}

static long __vsyscall(3) venosys_1(void)
{
	return -ENOSYS;
}

#ifdef CONFIG_SYSCTL
static ctl_table kernel_table2[] = {
	{ .procname = "vsyscall64",
	  .data = &vsyscall_gtod_data.sysctl_enabled, .maxlen = sizeof(int),
	  .mode = 0644,
	  .proc_handler = proc_dointvec },
	{}
};

static ctl_table kernel_root_table2[] = {
	{ .procname = "kernel", .mode = 0555,
	  .child = kernel_table2 },
	{}
};
#endif

/* Assume __initcall executes before all user space. Hopefully kmod
   doesn't violate that. We'll find out if it does. */
static void __cpuinit vsyscall_set_cpu(int cpu)
{
	unsigned long d;
	unsigned long node = 0;
#ifdef CONFIG_NUMA
	node = cpu_to_node(cpu);
#endif
	if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
		write_rdtscp_aux((node << 12) | cpu);

	/* Store cpu number in limit so that it can be loaded quickly
	   in user space in vgetcpu.
	   12 bits for the CPU and 8 bits for the node. */
	d = 0x0f40000000000ULL;
	d |= cpu;
	d |= (node & 0xf) << 12;
	d |= (node >> 4) << 48;
	write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
}

static void __cpuinit cpu_vsyscall_init(void *arg)
{
	/* preemption should be already off */
	vsyscall_set_cpu(raw_smp_processor_id());
}

static int __cpuinit
cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
{
	long cpu = (long)arg;
	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
		smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
	return NOTIFY_DONE;
}

void __init map_vsyscall(void)
{
	extern char __vsyscall_0;
	unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);

	/* Note that VSYSCALL_MAPPED_PAGES must agree with the code below. */
	__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
}

static int __init vsyscall_init(void)
{
	BUG_ON(((unsigned long) &vgettimeofday !=
			VSYSCALL_ADDR(__NR_vgettimeofday)));
	BUG_ON((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime));
	BUG_ON((VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE)));
	BUG_ON((unsigned long) &vgetcpu != VSYSCALL_ADDR(__NR_vgetcpu));
#ifdef CONFIG_SYSCTL
	register_sysctl_table(kernel_root_table2);
#endif
	on_each_cpu(cpu_vsyscall_init, NULL, 1);
	/* notifier priority > KVM */
	hotcpu_notifier(cpu_vsyscall_notifier, 30);
	return 0;
}

__initcall(vsyscall_init);