aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/pvclock.c
blob: 4f9c55f3a7c0f7e2590a5e248428bd19aa0d5c37 (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
/*  paravirtual clock -- common code used by kvm/xen

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <linux/kernel.h>
#include <linux/percpu.h>
#include <asm/pvclock.h>

/*
 * These are perodically updated
 *    xen: magic shared_info page
 *    kvm: gpa registered via msr
 * and then copied here.
 */
struct pvclock_shadow_time {
	u64 tsc_timestamp;     /* TSC at last update of time vals.  */
	u64 system_timestamp;  /* Time, in nanosecs, since boot.    */
	u32 tsc_to_nsec_mul;
	int tsc_shift;
	u32 version;
};

/*
 * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
 * yielding a 64-bit result.
 */
static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
{
	u64 product;
#ifdef __i386__
	u32 tmp1, tmp2;
#endif

	if (shift < 0)
		delta >>= -shift;
	else
		delta <<= shift;

#ifdef __i386__
	__asm__ (
		"mul  %5       ; "
		"mov  %4,%%eax ; "
		"mov  %%edx,%4 ; "
		"mul  %5       ; "
		"xor  %5,%5    ; "
		"add  %4,%%eax ; "
		"adc  %5,%%edx ; "
		: "=A" (product), "=r" (tmp1), "=r" (tmp2)
		: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
#elif __x86_64__
	__asm__ (
		"mul %%rdx ; shrd $32,%%rdx,%%rax"
		: "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
#else
#error implement me!
#endif

	return product;
}

static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
{
	u64 delta = native_read_tsc() - shadow->tsc_timestamp;
	return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
}

/*
 * Reads a consistent set of time-base values from hypervisor,
 * into a shadow data area.
 */
static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
					struct pvclock_vcpu_time_info *src)
{
	do {
		dst->version = src->version;
		rmb();		/* fetch version before data */
		dst->tsc_timestamp     = src->tsc_timestamp;
		dst->system_timestamp  = src->system_time;
		dst->tsc_to_nsec_mul   = src->tsc_to_system_mul;
		dst->tsc_shift         = src->tsc_shift;
		rmb();		/* test version after fetching data */
	} while ((src->version & 1) || (dst->version != src->version));

	return dst->version;
}

unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
{
	u64 pv_tsc_khz = 1000000ULL << 32;

	do_div(pv_tsc_khz, src->tsc_to_system_mul);
	if (src->tsc_shift < 0)
		pv_tsc_khz <<= -src->tsc_shift;
	else
		pv_tsc_khz >>= src->tsc_shift;
	return pv_tsc_khz;
}

cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
{
	struct pvclock_shadow_time shadow;
	unsigned version;
	cycle_t ret, offset;

	do {
		version = pvclock_get_time_values(&shadow, src);
		barrier();
		offset = pvclock_get_nsec_offset(&shadow);
		ret = shadow.system_timestamp + offset;
		barrier();
	} while (version != src->version);

	return ret;
}

void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
			    struct pvclock_vcpu_time_info *vcpu_time,
			    struct timespec *ts)
{
	u32 version;
	u64 delta;
	struct timespec now;

	/* get wallclock at system boot */
	do {
		version = wall_clock->version;
		rmb();		/* fetch version before time */
		now.tv_sec  = wall_clock->sec;
		now.tv_nsec = wall_clock->nsec;
		rmb();		/* fetch time before checking version */
	} while ((wall_clock->version & 1) || (version != wall_clock->version));

	delta = pvclock_clocksource_read(vcpu_time);	/* time since system boot */
	delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;

	now.tv_nsec = do_div(delta, NSEC_PER_SEC);
	now.tv_sec = delta;

	set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
}