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