arch/x86/kernel/vsyscall_64.c

   1 /*
   2  *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
   3  *  Copyright 2003 Andi Kleen, SuSE Labs.
   4  *
   5  *  Thanks to hpa@transmeta.com for some useful hint.
   6  *  Special thanks to Ingo Molnar for his early experience with
   7  *  a different vsyscall implementation for Linux/IA32 and for the name.
   8  *
   9  *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
  10  *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
  11  *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
  12  *  jumping out of line if necessary. We cannot add more with this
  13  *  mechanism because older kernels won't return -ENOSYS.
  14  *  If we want more than four we need a vDSO.
  15  *
  16  *  Note: the concept clashes with user mode linux. If you use UML and
  17  *  want per guest time just set the kernel.vsyscall64 sysctl to 0.
  18  */
  19
  20 /* Disable profiling for userspace code: */
  21 #define DISABLE_BRANCH_PROFILING
  22
  23 #include <linux/time.h>
  24 #include <linux/init.h>
  25 #include <linux/kernel.h>
  26 #include <linux/timer.h>
  27 #include <linux/seqlock.h>
  28 #include <linux/jiffies.h>
  29 #include <linux/sysctl.h>
  30 #include <linux/clocksource.h>
  31 #include <linux/getcpu.h>
  32 #include <linux/cpu.h>
  33 #include <linux/smp.h>
  34 #include <linux/notifier.h>
  35
  36 #include <asm/vsyscall.h>
  37 #include <asm/pgtable.h>
  38 #include <asm/page.h>
  39 #include <asm/unistd.h>
  40 #include <asm/fixmap.h>
  41 #include <asm/errno.h>
  42 #include <asm/io.h>
  43 #include <asm/segment.h>
  44 #include <asm/desc.h>
  45 #include <asm/topology.h>
  46 #include <asm/vgtod.h>
  47
  48 #define __vsyscall(nr) \
  49                 __attribute__ ((unused, __section__(".vsyscall_" #nr))) notrace
  50 #define __syscall_clobber "r11","cx","memory"
  51
  52 /*
  53  * vsyscall_gtod_data contains data that is :
  54  * - readonly from vsyscalls
  55  * - written by timer interrupt or systcl (/proc/sys/kernel/vsyscall64)
  56  * Try to keep this structure as small as possible to avoid cache line ping pongs
  57  */
  58 int __vgetcpu_mode __section_vgetcpu_mode;
  59
  60 struct vsyscall_gtod_data __vsyscall_gtod_data __section_vsyscall_gtod_data =
  61 {
  62         .lock = SEQLOCK_UNLOCKED,
  63         .sysctl_enabled = 1,
  64 };
  65
  66 void update_vsyscall_tz(void)
  67 {
  68         unsigned long flags;
  69
  70         write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
  71         /* sys_tz has changed */
  72         vsyscall_gtod_data.sys_tz = sys_tz;
  73         write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
  74 }
  75
  76 void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
  77 {
  78         unsigned long flags;
  79
  80         write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
  81         /* copy vsyscall data */
  82         vsyscall_gtod_data.clock.vread = clock->vread;
  83         vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
  84         vsyscall_gtod_data.clock.mask = clock->mask;
  85         vsyscall_gtod_data.clock.mult = clock->mult;
  86         vsyscall_gtod_data.clock.shift = clock->shift;
  87         vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
  88         vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
  89         vsyscall_gtod_data.wall_to_monotonic = wall_to_monotonic;
  90         write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
  91 }
  92
  93 /* RED-PEN may want to readd seq locking, but then the variable should be
  94  * write-once.
  95  */
  96 static __always_inline void do_get_tz(struct timezone * tz)
  97 {
  98         *tz = __vsyscall_gtod_data.sys_tz;
  99 }
 100
 101 static __always_inline int gettimeofday(struct timeval *tv, struct timezone *tz)
 102 {
 103         int ret;
 104         asm volatile("syscall"
 105                 : "=a" (ret)
 106                 : "0" (__NR_gettimeofday),"D" (tv),"S" (tz)
 107                 : __syscall_clobber );
 108         return ret;
 109 }
 110
 111 static __always_inline long time_syscall(long *t)
 112 {
 113         long secs;
 114         asm volatile("syscall"
 115                 : "=a" (secs)
 116                 : "0" (__NR_time),"D" (t) : __syscall_clobber);
 117         return secs;
 118 }
 119
 120 static __always_inline void do_vgettimeofday(struct timeval * tv)
 121 {
 122         cycle_t now, base, mask, cycle_delta;
 123         unsigned seq;
 124         unsigned long mult, shift, nsec;
 125         cycle_t (*vread)(void);
 126         do {
 127                 seq = read_seqbegin(&__vsyscall_gtod_data.lock);
 128
 129                 vread = __vsyscall_gtod_data.clock.vread;
 130                 if (unlikely(!__vsyscall_gtod_data.sysctl_enabled || !vread)) {
 131                         gettimeofday(tv,NULL);
 132                         return;
 133                 }
 134
 135                 now = vread();
 136                 base = __vsyscall_gtod_data.clock.cycle_last;
 137                 mask = __vsyscall_gtod_data.clock.mask;
 138                 mult = __vsyscall_gtod_data.clock.mult;
 139                 shift = __vsyscall_gtod_data.clock.shift;
 140
 141                 tv->tv_sec = __vsyscall_gtod_data.wall_time_sec;
 142                 nsec = __vsyscall_gtod_data.wall_time_nsec;
 143         } while (read_seqretry(&__vsyscall_gtod_data.lock, seq));
 144
 145         /* calculate interval: */
 146         cycle_delta = (now - base) & mask;
 147         /* convert to nsecs: */
 148         nsec += (cycle_delta * mult) >> shift;
 149
 150         while (nsec >= NSEC_PER_SEC) {
 151                 tv->tv_sec += 1;
 152                 nsec -= NSEC_PER_SEC;
 153         }
 154         tv->tv_usec = nsec / NSEC_PER_USEC;
 155 }
 156
 157 int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
 158 {
 159         if (tv)
 160                 do_vgettimeofday(tv);
 161         if (tz)
 162                 do_get_tz(tz);
 163         return 0;
 164 }
 165
 166 /* This will break when the xtime seconds get inaccurate, but that is
 167  * unlikely */
 168 time_t __vsyscall(1) vtime(time_t *t)
 169 {
 170         struct timeval tv;
 171         time_t result;
 172         if (unlikely(!__vsyscall_gtod_data.sysctl_enabled))
 173                 return time_syscall(t);
 174
 175         vgettimeofday(&tv, NULL);
 176         result = tv.tv_sec;
 177         if (t)
 178                 *t = result;
 179         return result;
 180 }
 181
 182 /* Fast way to get current CPU and node.
 183    This helps to do per node and per CPU caches in user space.
 184    The result is not guaranteed without CPU affinity, but usually
 185    works out because the scheduler tries to keep a thread on the same
 186    CPU.
 187
 188    tcache must point to a two element sized long array.
 189    All arguments can be NULL. */
 190 long __vsyscall(2)
 191 vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
 192 {
 193         unsigned int p;
 194         unsigned long j = 0;
 195
 196         /* Fast cache - only recompute value once per jiffies and avoid
 197            relatively costly rdtscp/cpuid otherwise.
 198            This works because the scheduler usually keeps the process
 199            on the same CPU and this syscall doesn't guarantee its
 200            results anyways.
 201            We do this here because otherwise user space would do it on
 202            its own in a likely inferior way (no access to jiffies).
 203            If you don't like it pass NULL. */
 204         if (tcache && tcache->blob[0] == (j = __jiffies)) {
 205                 p = tcache->blob[1];
 206         } else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
 207                 /* Load per CPU data from RDTSCP */
 208                 native_read_tscp(&p);
 209         } else {
 210                 /* Load per CPU data from GDT */
 211                 asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
 212         }
 213         if (tcache) {
 214                 tcache->blob[0] = j;
 215                 tcache->blob[1] = p;
 216         }
 217         if (cpu)
 218                 *cpu = p & 0xfff;
 219         if (node)
 220                 *node = p >> 12;
 221         return 0;
 222 }
 223
 224 static long __vsyscall(3) venosys_1(void)
 225 {
 226         return -ENOSYS;
 227 }
 228
 229 #ifdef CONFIG_SYSCTL
 230
 231 static int
 232 vsyscall_sysctl_change(ctl_table *ctl, int write, struct file * filp,
 233                        void __user *buffer, size_t *lenp, loff_t *ppos)
 234 {
 235         return proc_dointvec(ctl, write, filp, buffer, lenp, ppos);
 236 }
 237
 238 static ctl_table kernel_table2[] = {
 239         { .procname = "vsyscall64",
 240           .data = &vsyscall_gtod_data.sysctl_enabled, .maxlen = sizeof(int),
 241           .mode = 0644,
 242           .proc_handler = vsyscall_sysctl_change },
 243         {}
 244 };
 245
 246 static ctl_table kernel_root_table2[] = {
 247         { .ctl_name = CTL_KERN, .procname = "kernel", .mode = 0555,
 248           .child = kernel_table2 },
 249         {}
 250 };
 251 #endif
 252
 253 /* Assume __initcall executes before all user space. Hopefully kmod
 254    doesn't violate that. We'll find out if it does. */
 255 static void __cpuinit vsyscall_set_cpu(int cpu)
 256 {
 257         unsigned long d;
 258         unsigned long node = 0;
 259 #ifdef CONFIG_NUMA
 260         node = cpu_to_node(cpu);
 261 #endif
 262         if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
 263                 write_rdtscp_aux((node << 12) | cpu);
 264
 265         /* Store cpu number in limit so that it can be loaded quickly
 266            in user space in vgetcpu.
 267            12 bits for the CPU and 8 bits for the node. */
 268         d = 0x0f40000000000ULL;
 269         d |= cpu;
 270         d |= (node & 0xf) << 12;
 271         d |= (node >> 4) << 48;
 272         write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 273 }
 274
 275 static void __cpuinit cpu_vsyscall_init(void *arg)
 276 {
 277         /* preemption should be already off */
 278         vsyscall_set_cpu(raw_smp_processor_id());
 279 }
 280
 281 static int __cpuinit
 282 cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
 283 {
 284         long cpu = (long)arg;
 285         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
 286                 smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
 287         return NOTIFY_DONE;
 288 }
 289
 290 void __init map_vsyscall(void)
 291 {
 292         extern char __vsyscall_0;
 293         unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
 294
 295         /* Note that VSYSCALL_MAPPED_PAGES must agree with the code below. */
 296         __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
 297 }
 298
 299 static int __init vsyscall_init(void)
 300 {
 301         BUG_ON(((unsigned long) &vgettimeofday !=
 302                         VSYSCALL_ADDR(__NR_vgettimeofday)));
 303         BUG_ON((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime));
 304         BUG_ON((VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE)));
 305         BUG_ON((unsigned long) &vgetcpu != VSYSCALL_ADDR(__NR_vgetcpu));
 306 #ifdef CONFIG_SYSCTL
 307         register_sysctl_table(kernel_root_table2);
 308 #endif
 309         on_each_cpu(cpu_vsyscall_init, NULL, 1);
 310         hotcpu_notifier(cpu_vsyscall_notifier, 0);
 311         return 0;
 312 }
 313
 314 __initcall(vsyscall_init);