LXR linux/arch/x86/kernel/pvclock.c

   1/*  paravirtual clock -- common code used by kvm/xen
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; either version 2 of the License, or
   6    (at your option) any later version.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program; if not, write to the Free Software
  15    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  16*/
  17
  18#include <linux/kernel.h>
  19#include <linux/percpu.h>
  20#include <asm/pvclock.h>
  21
  22/*
  23 * These are perodically updated
  24 *    xen: magic shared_info page
  25 *    kvm: gpa registered via msr
  26 * and then copied here.
  27 */
  28struct pvclock_shadow_time {
  29        u64 tsc_timestamp;     /* TSC at last update of time vals.  */
  30        u64 system_timestamp;  /* Time, in nanosecs, since boot.    */
  31        u32 tsc_to_nsec_mul;
  32        int tsc_shift;
  33        u32 version;
  34};
  35
  36/*
  37 * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
  38 * yielding a 64-bit result.
  39 */
  40static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
  41{
  42        u64 product;
  43#ifdef __i386__
  44        u32 tmp1, tmp2;
  45#endif
  46
  47        if (shift < 0)
  48                delta >>= -shift;
  49        else
  50                delta <<= shift;
  51
  52#ifdef __i386__
  53        __asm__ (
  54                "mul  %5       ; "
  55                "mov  %4,%%eax ; "
  56                "mov  %%edx,%4 ; "
  57                "mul  %5       ; "
  58                "xor  %5,%5    ; "
  59                "add  %4,%%eax ; "
  60                "adc  %5,%%edx ; "
  61                : "=A" (product), "=r" (tmp1), "=r" (tmp2)
  62                : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
  63#elif __x86_64__
  64        __asm__ (
  65                "mul %%rdx ; shrd $32,%%rdx,%%rax"
  66                : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
  67#else
  68#error implement me!
  69#endif
  70
  71        return product;
  72}
  73
  74static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
  75{
  76        u64 delta = native_read_tsc() - shadow->tsc_timestamp;
  77        return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
  78}
  79
  80/*
  81 * Reads a consistent set of time-base values from hypervisor,
  82 * into a shadow data area.
  83 */
  84static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
  85                                        struct pvclock_vcpu_time_info *src)
  86{
  87        do {
  88                dst->version = src->version;
  89                rmb();          /* fetch version before data */
  90                dst->tsc_timestamp     = src->tsc_timestamp;
  91                dst->system_timestamp  = src->system_time;
  92                dst->tsc_to_nsec_mul   = src->tsc_to_system_mul;
  93                dst->tsc_shift         = src->tsc_shift;
  94                rmb();          /* test version after fetching data */
  95        } while ((src->version & 1) || (dst->version != src->version));
  96
  97        return dst->version;
  98}
  99
 100cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 101{
 102        struct pvclock_shadow_time shadow;
 103        unsigned version;
 104        cycle_t ret, offset;
 105
 106        do {
 107                version = pvclock_get_time_values(&shadow, src);
 108                barrier();
 109                offset = pvclock_get_nsec_offset(&shadow);
 110                ret = shadow.system_timestamp + offset;
 111                barrier();
 112        } while (version != src->version);
 113
 114        return ret;
 115}
 116
 117void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 118                            struct pvclock_vcpu_time_info *vcpu_time,
 119                            struct timespec *ts)
 120{
 121        u32 version;
 122        u64 delta;
 123        struct timespec now;
 124
 125        /* get wallclock at system boot */
 126        do {
 127                version = wall_clock->version;
 128                rmb();          /* fetch version before time */
 129                now.tv_sec  = wall_clock->sec;
 130                now.tv_nsec = wall_clock->nsec;
 131                rmb();          /* fetch time before checking version */
 132        } while ((wall_clock->version & 1) || (version != wall_clock->version));
 133
 134        delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 135        delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 136
 137        now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 138        now.tv_sec = delta;
 139
 140        set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 141}
 142