arch/x86_64/kernel/vsyscall.c

   1 /*
   2  *  linux/arch/x86_64/kernel/vsyscall.c
   3  *
   4  *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
   5  *  Copyright 2003 Andi Kleen, SuSE Labs.
   6  *
   7  *  Thanks to hpa@transmeta.com for some useful hint.
   8  *  Special thanks to Ingo Molnar for his early experience with
   9  *  a different vsyscall implementation for Linux/IA32 and for the name.
  10  *
  11  *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
  12  *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
  13  *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
  14  *  jumping out of line if necessary. We cannot add more with this
  15  *  mechanism because older kernels won't return -ENOSYS.
  16  *  If we want more than four we need a vDSO.
  17  *
  18  *  Note: the concept clashes with user mode linux. If you use UML and
  19  *  want per guest time just set the kernel.vsyscall64 sysctl to 0.
  20  */
  21
  22 #include <linux/time.h>
  23 #include <linux/init.h>
  24 #include <linux/kernel.h>
  25 #include <linux/timer.h>
  26 #include <linux/seqlock.h>
  27 #include <linux/jiffies.h>
  28 #include <linux/sysctl.h>
  29
  30 #include <asm/vsyscall.h>
  31 #include <asm/pgtable.h>
  32 #include <asm/page.h>
  33 #include <asm/fixmap.h>
  34 #include <asm/errno.h>
  35 #include <asm/io.h>
  36
  37 #define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))
  38
  39 int __sysctl_vsyscall __section_sysctl_vsyscall = 1;
  40 seqlock_t __xtime_lock __section_xtime_lock = SEQLOCK_UNLOCKED;
  41
  42 #include <asm/unistd.h>
  43
  44 static __always_inline void timeval_normalize(struct timeval * tv)
  45 {
  46         time_t __sec;
  47
  48         __sec = tv->tv_usec / 1000000;
  49         if (__sec) {
  50                 tv->tv_usec %= 1000000;
  51                 tv->tv_sec += __sec;
  52         }
  53 }
  54
  55 static __always_inline void do_vgettimeofday(struct timeval * tv)
  56 {
  57         long sequence, t;
  58         unsigned long sec, usec;
  59
  60         do {
  61                 sequence = read_seqbegin(&__xtime_lock);
  62
  63                 sec = __xtime.tv_sec;
  64                 usec = (__xtime.tv_nsec / 1000) +
  65                         (__jiffies - __wall_jiffies) * (1000000 / HZ);
  66
  67                 if (__vxtime.mode != VXTIME_HPET) {
  68                         t = get_cycles_sync();
  69                         if (t < __vxtime.last_tsc)
  70                                 t = __vxtime.last_tsc;
  71                         usec += ((t - __vxtime.last_tsc) *
  72                                  __vxtime.tsc_quot) >> 32;
  73                         /* See comment in x86_64 do_gettimeofday. */
  74                 } else {
  75                         usec += ((readl((void *)fix_to_virt(VSYSCALL_HPET) + 0xf0) -
  76                                   __vxtime.last) * __vxtime.quot) >> 32;
  77                 }
  78         } while (read_seqretry(&__xtime_lock, sequence));
  79
  80         tv->tv_sec = sec + usec / 1000000;
  81         tv->tv_usec = usec % 1000000;
  82 }
  83
  84 /* RED-PEN may want to readd seq locking, but then the variable should be write-once. */
  85 static __always_inline void do_get_tz(struct timezone * tz)
  86 {
  87         *tz = __sys_tz;
  88 }
  89
  90 static __always_inline int gettimeofday(struct timeval *tv, struct timezone *tz)
  91 {
  92         int ret;
  93         asm volatile("vsysc2: syscall"
  94                 : "=a" (ret)
  95                 : "0" (__NR_gettimeofday),"D" (tv),"S" (tz) : __syscall_clobber );
  96         return ret;
  97 }
  98
  99 static __always_inline long time_syscall(long *t)
 100 {
 101         long secs;
 102         asm volatile("vsysc1: syscall"
 103                 : "=a" (secs)
 104                 : "0" (__NR_time),"D" (t) : __syscall_clobber);
 105         return secs;
 106 }
 107
 108 int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
 109 {
 110         if (unlikely(!__sysctl_vsyscall))
 111                 return gettimeofday(tv,tz);
 112         if (tv)
 113                 do_vgettimeofday(tv);
 114         if (tz)
 115                 do_get_tz(tz);
 116         return 0;
 117 }
 118
 119 /* This will break when the xtime seconds get inaccurate, but that is
 120  * unlikely */
 121 time_t __vsyscall(1) vtime(time_t *t)
 122 {
 123         if (unlikely(!__sysctl_vsyscall))
 124                 return time_syscall(t);
 125         else if (t)
 126                 *t = __xtime.tv_sec;
 127         return __xtime.tv_sec;
 128 }
 129
 130 long __vsyscall(2) venosys_0(void)
 131 {
 132         return -ENOSYS;
 133 }
 134
 135 long __vsyscall(3) venosys_1(void)
 136 {
 137         return -ENOSYS;
 138 }
 139
 140 #ifdef CONFIG_SYSCTL
 141
 142 #define SYSCALL 0x050f
 143 #define NOP2    0x9090
 144
 145 /*
 146  * NOP out syscall in vsyscall page when not needed.
 147  */
 148 static int vsyscall_sysctl_change(ctl_table *ctl, int write, struct file * filp,
 149                         void __user *buffer, size_t *lenp, loff_t *ppos)
 150 {
 151         extern u16 vsysc1, vsysc2;
 152         u16 *map1, *map2;
 153         int ret = proc_dointvec(ctl, write, filp, buffer, lenp, ppos);
 154         if (!write)
 155                 return ret;
 156         /* gcc has some trouble with __va(__pa()), so just do it this
 157            way. */
 158         map1 = ioremap(__pa_symbol(&vsysc1), 2);
 159         if (!map1)
 160                 return -ENOMEM;
 161         map2 = ioremap(__pa_symbol(&vsysc2), 2);
 162         if (!map2) {
 163                 ret = -ENOMEM;
 164                 goto out;
 165         }
 166         if (!sysctl_vsyscall) {
 167                 *map1 = SYSCALL;
 168                 *map2 = SYSCALL;
 169         } else {
 170                 *map1 = NOP2;
 171                 *map2 = NOP2;
 172         }
 173         iounmap(map2);
 174 out:
 175         iounmap(map1);
 176         return ret;
 177 }
 178
 179 static int vsyscall_sysctl_nostrat(ctl_table *t, int __user *name, int nlen,
 180                                 void __user *oldval, size_t __user *oldlenp,
 181                                 void __user *newval, size_t newlen,
 182                                 void **context)
 183 {
 184         return -ENOSYS;
 185 }
 186
 187 static ctl_table kernel_table2[] = {
 188         { .ctl_name = 99, .procname = "vsyscall64",
 189           .data = &sysctl_vsyscall, .maxlen = sizeof(int), .mode = 0644,
 190           .strategy = vsyscall_sysctl_nostrat,
 191           .proc_handler = vsyscall_sysctl_change },
 192         { 0, }
 193 };
 194
 195 static ctl_table kernel_root_table2[] = {
 196         { .ctl_name = CTL_KERN, .procname = "kernel", .mode = 0555,
 197           .child = kernel_table2 },
 198         { 0 },
 199 };
 200
 201 #endif
 202
 203 static void __init map_vsyscall(void)
 204 {
 205         extern char __vsyscall_0;
 206         unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
 207
 208         __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
 209 }
 210
 211 static int __init vsyscall_init(void)
 212 {
 213         BUG_ON(((unsigned long) &vgettimeofday !=
 214                         VSYSCALL_ADDR(__NR_vgettimeofday)));
 215         BUG_ON((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime));
 216         BUG_ON((VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE)));
 217         map_vsyscall();
 218 #ifdef CONFIG_SYSCTL
 219         register_sysctl_table(kernel_root_table2, 0);
 220 #endif
 221         return 0;
 222 }
 223
 224 __initcall(vsyscall_init);