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Linux/arch/x86/kernel/pvclock.c

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  1 /*  paravirtual clock -- common code used by kvm/xen
  2 
  3     This program is free software; you can redistribute it and/or modify
  4     it under the terms of the GNU General Public License as published by
  5     the Free Software Foundation; either version 2 of the License, or
  6     (at your option) any later version.
  7 
  8     This program is distributed in the hope that it will be useful,
  9     but WITHOUT ANY WARRANTY; without even the implied warranty of
 10     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 11     GNU General Public License for more details.
 12 
 13     You should have received a copy of the GNU General Public License
 14     along with this program; if not, write to the Free Software
 15     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 16 */
 17 
 18 #include <linux/kernel.h>
 19 #include <linux/percpu.h>
 20 #include <linux/notifier.h>
 21 #include <linux/sched.h>
 22 #include <linux/gfp.h>
 23 #include <linux/bootmem.h>
 24 #include <asm/fixmap.h>
 25 #include <asm/pvclock.h>
 26 
 27 static u8 valid_flags __read_mostly = 0;
 28 
 29 void pvclock_set_flags(u8 flags)
 30 {
 31         valid_flags = flags;
 32 }
 33 
 34 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
 35 {
 36         u64 pv_tsc_khz = 1000000ULL << 32;
 37 
 38         do_div(pv_tsc_khz, src->tsc_to_system_mul);
 39         if (src->tsc_shift < 0)
 40                 pv_tsc_khz <<= -src->tsc_shift;
 41         else
 42                 pv_tsc_khz >>= src->tsc_shift;
 43         return pv_tsc_khz;
 44 }
 45 
 46 static atomic64_t last_value = ATOMIC64_INIT(0);
 47 
 48 void pvclock_resume(void)
 49 {
 50         atomic64_set(&last_value, 0);
 51 }
 52 
 53 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
 54 {
 55         unsigned version;
 56         cycle_t ret;
 57         u8 flags;
 58 
 59         do {
 60                 version = __pvclock_read_cycles(src, &ret, &flags);
 61         } while ((src->version & 1) || version != src->version);
 62 
 63         return flags & valid_flags;
 64 }
 65 
 66 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 67 {
 68         unsigned version;
 69         cycle_t ret;
 70         u64 last;
 71         u8 flags;
 72 
 73         do {
 74                 version = __pvclock_read_cycles(src, &ret, &flags);
 75         } while ((src->version & 1) || version != src->version);
 76 
 77         if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
 78                 (flags & PVCLOCK_TSC_STABLE_BIT))
 79                 return ret;
 80 
 81         /*
 82          * Assumption here is that last_value, a global accumulator, always goes
 83          * forward. If we are less than that, we should not be much smaller.
 84          * We assume there is an error marging we're inside, and then the correction
 85          * does not sacrifice accuracy.
 86          *
 87          * For reads: global may have changed between test and return,
 88          * but this means someone else updated poked the clock at a later time.
 89          * We just need to make sure we are not seeing a backwards event.
 90          *
 91          * For updates: last_value = ret is not enough, since two vcpus could be
 92          * updating at the same time, and one of them could be slightly behind,
 93          * making the assumption that last_value always go forward fail to hold.
 94          */
 95         last = atomic64_read(&last_value);
 96         do {
 97                 if (ret < last)
 98                         return last;
 99                 last = atomic64_cmpxchg(&last_value, last, ret);
100         } while (unlikely(last != ret));
101 
102         return ret;
103 }
104 
105 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
106                             struct pvclock_vcpu_time_info *vcpu_time,
107                             struct timespec *ts)
108 {
109         u32 version;
110         u64 delta;
111         struct timespec now;
112 
113         /* get wallclock at system boot */
114         do {
115                 version = wall_clock->version;
116                 rmb();          /* fetch version before time */
117                 now.tv_sec  = wall_clock->sec;
118                 now.tv_nsec = wall_clock->nsec;
119                 rmb();          /* fetch time before checking version */
120         } while ((wall_clock->version & 1) || (version != wall_clock->version));
121 
122         delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
123         delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
124 
125         now.tv_nsec = do_div(delta, NSEC_PER_SEC);
126         now.tv_sec = delta;
127 
128         set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
129 }
130 
131 static struct pvclock_vsyscall_time_info *pvclock_vdso_info;
132 
133 static struct pvclock_vsyscall_time_info *
134 pvclock_get_vsyscall_user_time_info(int cpu)
135 {
136         if (!pvclock_vdso_info) {
137                 BUG();
138                 return NULL;
139         }
140 
141         return &pvclock_vdso_info[cpu];
142 }
143 
144 struct pvclock_vcpu_time_info *pvclock_get_vsyscall_time_info(int cpu)
145 {
146         return &pvclock_get_vsyscall_user_time_info(cpu)->pvti;
147 }
148 
149 #ifdef CONFIG_X86_64
150 static int pvclock_task_migrate(struct notifier_block *nb, unsigned long l,
151                                 void *v)
152 {
153         struct task_migration_notifier *mn = v;
154         struct pvclock_vsyscall_time_info *pvti;
155 
156         pvti = pvclock_get_vsyscall_user_time_info(mn->from_cpu);
157 
158         /* this is NULL when pvclock vsyscall is not initialized */
159         if (unlikely(pvti == NULL))
160                 return NOTIFY_DONE;
161 
162         pvti->migrate_count++;
163 
164         return NOTIFY_DONE;
165 }
166 
167 static struct notifier_block pvclock_migrate = {
168         .notifier_call = pvclock_task_migrate,
169 };
170 
171 /*
172  * Initialize the generic pvclock vsyscall state.  This will allocate
173  * a/some page(s) for the per-vcpu pvclock information, set up a
174  * fixmap mapping for the page(s)
175  */
176 
177 int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
178                                  int size)
179 {
180         int idx;
181 
182         WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE);
183 
184         pvclock_vdso_info = i;
185 
186         for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) {
187                 __set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx,
188                              __pa(i) + (idx*PAGE_SIZE),
189                              PAGE_KERNEL_VVAR);
190         }
191 
192 
193         register_task_migration_notifier(&pvclock_migrate);
194 
195         return 0;
196 }
197 #endif
198 

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