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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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408 lines
9.8 KiB
C
408 lines
9.8 KiB
C
![]() |
/*
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* Xen time implementation.
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*
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* This is implemented in terms of a clocksource driver which uses
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* the hypervisor clock as a nanosecond timebase, and a clockevent
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* driver which uses the hypervisor's timer mechanism.
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*
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* Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
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*/
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#include <linux/kernel.h>
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#include <linux/interrupt.h>
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#include <linux/clocksource.h>
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#include <linux/clockchips.h>
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#include <asm/xen/hypervisor.h>
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#include <asm/xen/hypercall.h>
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#include <xen/events.h>
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#include <xen/interface/xen.h>
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#include <xen/interface/vcpu.h>
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#include "xen-ops.h"
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#define XEN_SHIFT 22
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/* Xen may fire a timer up to this many ns early */
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#define TIMER_SLOP 100000
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/* These are perodically updated in shared_info, and then copied here. */
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struct shadow_time_info {
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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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static DEFINE_PER_CPU(struct shadow_time_info, shadow_time);
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unsigned long xen_cpu_khz(void)
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{
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u64 cpu_khz = 1000000ULL << 32;
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const struct vcpu_time_info *info =
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&HYPERVISOR_shared_info->vcpu_info[0].time;
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do_div(cpu_khz, info->tsc_to_system_mul);
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if (info->tsc_shift < 0)
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cpu_khz <<= -info->tsc_shift;
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else
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cpu_khz >>= info->tsc_shift;
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return cpu_khz;
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}
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/*
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* Reads a consistent set of time-base values from Xen, into a shadow data
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* area.
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*/
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static void get_time_values_from_xen(void)
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{
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struct vcpu_time_info *src;
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struct shadow_time_info *dst;
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preempt_disable();
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/* src is shared memory with the hypervisor, so we need to
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make sure we get a consistent snapshot, even in the face of
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being preempted. */
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src = &__get_cpu_var(xen_vcpu)->time;
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dst = &__get_cpu_var(shadow_time);
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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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preempt_enable();
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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 get_nsec_offset(struct shadow_time_info *shadow)
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{
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u64 now, delta;
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rdtscll(now);
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delta = now - 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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cycle_t xen_clocksource_read(void)
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{
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struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
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cycle_t ret;
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get_time_values_from_xen();
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ret = shadow->system_timestamp + get_nsec_offset(shadow);
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put_cpu_var(shadow_time);
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return ret;
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}
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static void xen_read_wallclock(struct timespec *ts)
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{
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const struct shared_info *s = HYPERVISOR_shared_info;
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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 = s->wc_version;
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rmb(); /* fetch version before time */
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now.tv_sec = s->wc_sec;
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now.tv_nsec = s->wc_nsec;
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rmb(); /* fetch time before checking version */
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} while ((s->wc_version & 1) | (version ^ s->wc_version));
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delta = xen_clocksource_read(); /* 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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unsigned long xen_get_wallclock(void)
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{
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struct timespec ts;
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xen_read_wallclock(&ts);
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return ts.tv_sec;
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}
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int xen_set_wallclock(unsigned long now)
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{
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/* do nothing for domU */
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return -1;
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}
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static struct clocksource xen_clocksource __read_mostly = {
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.name = "xen",
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.rating = 400,
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.read = xen_clocksource_read,
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.mask = ~0,
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.mult = 1<<XEN_SHIFT, /* time directly in nanoseconds */
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.shift = XEN_SHIFT,
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.flags = CLOCK_SOURCE_IS_CONTINUOUS,
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};
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/*
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Xen clockevent implementation
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Xen has two clockevent implementations:
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The old timer_op one works with all released versions of Xen prior
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to version 3.0.4. This version of the hypervisor provides a
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single-shot timer with nanosecond resolution. However, sharing the
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same event channel is a 100Hz tick which is delivered while the
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vcpu is running. We don't care about or use this tick, but it will
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cause the core time code to think the timer fired too soon, and
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will end up resetting it each time. It could be filtered, but
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doing so has complications when the ktime clocksource is not yet
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the xen clocksource (ie, at boot time).
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The new vcpu_op-based timer interface allows the tick timer period
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to be changed or turned off. The tick timer is not useful as a
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periodic timer because events are only delivered to running vcpus.
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The one-shot timer can report when a timeout is in the past, so
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set_next_event is capable of returning -ETIME when appropriate.
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This interface is used when available.
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*/
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/*
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Get a hypervisor absolute time. In theory we could maintain an
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offset between the kernel's time and the hypervisor's time, and
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apply that to a kernel's absolute timeout. Unfortunately the
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hypervisor and kernel times can drift even if the kernel is using
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the Xen clocksource, because ntp can warp the kernel's clocksource.
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*/
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static s64 get_abs_timeout(unsigned long delta)
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{
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return xen_clocksource_read() + delta;
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}
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static void xen_timerop_set_mode(enum clock_event_mode mode,
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struct clock_event_device *evt)
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{
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switch (mode) {
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case CLOCK_EVT_MODE_PERIODIC:
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/* unsupported */
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WARN_ON(1);
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break;
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case CLOCK_EVT_MODE_ONESHOT:
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break;
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case CLOCK_EVT_MODE_UNUSED:
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case CLOCK_EVT_MODE_SHUTDOWN:
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HYPERVISOR_set_timer_op(0); /* cancel timeout */
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break;
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}
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}
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static int xen_timerop_set_next_event(unsigned long delta,
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struct clock_event_device *evt)
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{
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WARN_ON(evt->mode != CLOCK_EVT_MODE_ONESHOT);
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if (HYPERVISOR_set_timer_op(get_abs_timeout(delta)) < 0)
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BUG();
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/* We may have missed the deadline, but there's no real way of
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knowing for sure. If the event was in the past, then we'll
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get an immediate interrupt. */
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return 0;
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}
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static const struct clock_event_device xen_timerop_clockevent = {
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.name = "xen",
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.features = CLOCK_EVT_FEAT_ONESHOT,
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.max_delta_ns = 0xffffffff,
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.min_delta_ns = TIMER_SLOP,
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.mult = 1,
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.shift = 0,
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.rating = 500,
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.set_mode = xen_timerop_set_mode,
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.set_next_event = xen_timerop_set_next_event,
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};
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static void xen_vcpuop_set_mode(enum clock_event_mode mode,
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struct clock_event_device *evt)
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{
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int cpu = smp_processor_id();
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switch (mode) {
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case CLOCK_EVT_MODE_PERIODIC:
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WARN_ON(1); /* unsupported */
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break;
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case CLOCK_EVT_MODE_ONESHOT:
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if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL))
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BUG();
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break;
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case CLOCK_EVT_MODE_UNUSED:
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case CLOCK_EVT_MODE_SHUTDOWN:
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if (HYPERVISOR_vcpu_op(VCPUOP_stop_singleshot_timer, cpu, NULL) ||
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HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL))
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BUG();
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break;
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}
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}
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static int xen_vcpuop_set_next_event(unsigned long delta,
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struct clock_event_device *evt)
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{
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int cpu = smp_processor_id();
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struct vcpu_set_singleshot_timer single;
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int ret;
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WARN_ON(evt->mode != CLOCK_EVT_MODE_ONESHOT);
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single.timeout_abs_ns = get_abs_timeout(delta);
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single.flags = VCPU_SSHOTTMR_future;
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ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single);
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BUG_ON(ret != 0 && ret != -ETIME);
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return ret;
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}
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static const struct clock_event_device xen_vcpuop_clockevent = {
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.name = "xen",
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.features = CLOCK_EVT_FEAT_ONESHOT,
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.max_delta_ns = 0xffffffff,
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.min_delta_ns = TIMER_SLOP,
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.mult = 1,
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.shift = 0,
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.rating = 500,
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.set_mode = xen_vcpuop_set_mode,
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.set_next_event = xen_vcpuop_set_next_event,
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};
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static const struct clock_event_device *xen_clockevent =
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&xen_timerop_clockevent;
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static DEFINE_PER_CPU(struct clock_event_device, xen_clock_events);
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static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
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{
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struct clock_event_device *evt = &__get_cpu_var(xen_clock_events);
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irqreturn_t ret;
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ret = IRQ_NONE;
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if (evt->event_handler) {
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evt->event_handler(evt);
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ret = IRQ_HANDLED;
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}
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return ret;
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}
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static void xen_setup_timer(int cpu)
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{
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const char *name;
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struct clock_event_device *evt;
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int irq;
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printk(KERN_INFO "installing Xen timer for CPU %d\n", cpu);
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name = kasprintf(GFP_KERNEL, "timer%d", cpu);
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if (!name)
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name = "<timer kasprintf failed>";
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irq = bind_virq_to_irqhandler(VIRQ_TIMER, cpu, xen_timer_interrupt,
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IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
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name, NULL);
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evt = &get_cpu_var(xen_clock_events);
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memcpy(evt, xen_clockevent, sizeof(*evt));
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evt->cpumask = cpumask_of_cpu(cpu);
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evt->irq = irq;
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clockevents_register_device(evt);
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put_cpu_var(xen_clock_events);
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}
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__init void xen_time_init(void)
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{
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int cpu = smp_processor_id();
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get_time_values_from_xen();
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clocksource_register(&xen_clocksource);
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if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
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/* Successfully turned off 100hz tick, so we have the
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vcpuop-based timer interface */
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printk(KERN_DEBUG "Xen: using vcpuop timer interface\n");
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xen_clockevent = &xen_vcpuop_clockevent;
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}
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/* Set initial system time with full resolution */
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xen_read_wallclock(&xtime);
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set_normalized_timespec(&wall_to_monotonic,
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-xtime.tv_sec, -xtime.tv_nsec);
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tsc_disable = 0;
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xen_setup_timer(cpu);
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}
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