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/* 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;
}
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);
}
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