Commit 7af192c9 authored by Gerd Hoffmann's avatar Gerd Hoffmann Committed by Avi Kivity

x86: Add structs and functions for paravirt clocksource

This patch adds structs for the paravirt clocksource ABI
used by both xen and kvm (pvclock-abi.h).

It also adds some helper functions to read system time and
wall clock time from a paravirtual clocksource (pvclock.[ch]).
They are based on the xen code.  They are enabled using

Subsequent patches of this series will put the code in use.
Signed-off-by: default avatarGerd Hoffmann <>
Acked-by: default avatarJeremy Fitzhardinge <>
Signed-off-by: default avatarAvi Kivity <>
parent a9b21b62
......@@ -410,6 +410,10 @@ config PARAVIRT
over full virtualization. However, when run without a hypervisor
the kernel is theoretically slower and slightly larger.
default n
......@@ -82,6 +82,7 @@ obj-$(CONFIG_VMI) += vmi_32.o vmiclock_32.o
obj-$(CONFIG_KVM_GUEST) += kvm.o
obj-$(CONFIG_KVM_CLOCK) += kvmclock.o
obj-$(CONFIG_PARAVIRT) += paravirt.o paravirt_patch_$(BITS).o
obj-$(CONFIG_PARAVIRT_CLOCK) += pvclock.o
obj-$(CONFIG_PCSPKR_PLATFORM) += pcspeaker.o
/* 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
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;
if (shift < 0)
delta >>= -shift;
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) );
#error implement me!
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);
offset = pvclock_get_nsec_offset(&shadow);
ret = shadow.system_timestamp + offset;
} 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);
#ifndef _ASM_X86_PVCLOCK_ABI_H_
#define _ASM_X86_PVCLOCK_ABI_H_
#ifndef __ASSEMBLY__
* These structs MUST NOT be changed.
* They are the ABI between hypervisor and guest OS.
* Both Xen and KVM are using this.
* pvclock_vcpu_time_info holds the system time and the tsc timestamp
* of the last update. So the guest can use the tsc delta to get a
* more precise system time. There is one per virtual cpu.
* pvclock_wall_clock references the point in time when the system
* time was zero (usually boot time), thus the guest calculates the
* current wall clock by adding the system time.
* Protocol for the "version" fields is: hypervisor raises it (making
* it uneven) before it starts updating the fields and raises it again
* (making it even) when it is done. Thus the guest can make sure the
* time values it got are consistent by checking the version before
* and after reading them.
struct pvclock_vcpu_time_info {
u32 version;
u32 pad0;
u64 tsc_timestamp;
u64 system_time;
u32 tsc_to_system_mul;
s8 tsc_shift;
u8 pad[3];
} __attribute__((__packed__)); /* 32 bytes */
struct pvclock_wall_clock {
u32 version;
u32 sec;
u32 nsec;
} __attribute__((__packed__));
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_PVCLOCK_ABI_H_ */
#ifndef _ASM_X86_PVCLOCK_H_
#define _ASM_X86_PVCLOCK_H_
#include <linux/clocksource.h>
#include <asm/pvclock-abi.h>
/* some helper functions for xen and kvm pv clock sources */
cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
struct pvclock_vcpu_time_info *vcpu,
struct timespec *ts);
#endif /* _ASM_X86_PVCLOCK_H_ */
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment