142 lines
3.8 KiB
C
142 lines
3.8 KiB
C
/* paravirtual clock -- common code used by kvm/xen
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/kernel.h>
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#include <linux/percpu.h>
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#include <asm/pvclock.h>
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/*
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* These are perodically updated
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* xen: magic shared_info page
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* kvm: gpa registered via msr
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* and then copied here.
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*/
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struct pvclock_shadow_time {
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u64 tsc_timestamp; /* TSC at last update of time vals. */
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u64 system_timestamp; /* Time, in nanosecs, since boot. */
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u32 tsc_to_nsec_mul;
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int tsc_shift;
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u32 version;
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};
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/*
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* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
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* yielding a 64-bit result.
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*/
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static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
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{
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u64 product;
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#ifdef __i386__
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u32 tmp1, tmp2;
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#endif
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if (shift < 0)
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delta >>= -shift;
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else
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delta <<= shift;
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#ifdef __i386__
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__asm__ (
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"mul %5 ; "
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"mov %4,%%eax ; "
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"mov %%edx,%4 ; "
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"mul %5 ; "
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"xor %5,%5 ; "
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"add %4,%%eax ; "
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"adc %5,%%edx ; "
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: "=A" (product), "=r" (tmp1), "=r" (tmp2)
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: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
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#elif __x86_64__
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__asm__ (
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"mul %%rdx ; shrd $32,%%rdx,%%rax"
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: "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
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#else
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#error implement me!
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#endif
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return product;
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}
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static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
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{
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u64 delta = native_read_tsc() - shadow->tsc_timestamp;
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return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
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}
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/*
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* Reads a consistent set of time-base values from hypervisor,
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* into a shadow data area.
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*/
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static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
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struct pvclock_vcpu_time_info *src)
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{
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do {
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dst->version = src->version;
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rmb(); /* fetch version before data */
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dst->tsc_timestamp = src->tsc_timestamp;
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dst->system_timestamp = src->system_time;
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dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
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dst->tsc_shift = src->tsc_shift;
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rmb(); /* test version after fetching data */
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} while ((src->version & 1) || (dst->version != src->version));
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return dst->version;
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}
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
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{
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struct pvclock_shadow_time shadow;
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unsigned version;
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cycle_t ret, offset;
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do {
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version = pvclock_get_time_values(&shadow, src);
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barrier();
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offset = pvclock_get_nsec_offset(&shadow);
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ret = shadow.system_timestamp + offset;
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barrier();
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} while (version != src->version);
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return ret;
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}
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
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struct pvclock_vcpu_time_info *vcpu_time,
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struct timespec *ts)
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{
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u32 version;
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u64 delta;
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struct timespec now;
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/* get wallclock at system boot */
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do {
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version = wall_clock->version;
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rmb(); /* fetch version before time */
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now.tv_sec = wall_clock->sec;
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now.tv_nsec = wall_clock->nsec;
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rmb(); /* fetch time before checking version */
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} while ((wall_clock->version & 1) || (version != wall_clock->version));
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delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
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delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
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now.tv_nsec = do_div(delta, NSEC_PER_SEC);
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now.tv_sec = delta;
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set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
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}
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