drivers/xen/time.c

   1 /*
   2  * Xen stolen ticks accounting.
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/kernel_stat.h>
   6 #include <linux/math64.h>
   7 #include <linux/gfp.h>
   8
   9 #include <asm/xen/hypervisor.h>
  10 #include <asm/xen/hypercall.h>
  11
  12 #include <xen/events.h>
  13 #include <xen/features.h>
  14 #include <xen/interface/xen.h>
  15 #include <xen/interface/vcpu.h>
  16 #include <xen/xen-ops.h>
  17
  18 /* runstate info updated by Xen */
  19 static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
  20
  21 /* return an consistent snapshot of 64-bit time/counter value */
  22 static u64 get64(const u64 *p)
  23 {
  24         u64 ret;
  25
  26         if (BITS_PER_LONG < 64) {
  27                 u32 *p32 = (u32 *)p;
  28                 u32 h, l, h2;
  29
  30                 /*
  31                  * Read high then low, and then make sure high is
  32                  * still the same; this will only loop if low wraps
  33                  * and carries into high.
  34                  * XXX some clean way to make this endian-proof?
  35                  */
  36                 do {
  37                         h = READ_ONCE(p32[1]);
  38                         l = READ_ONCE(p32[0]);
  39                         h2 = READ_ONCE(p32[1]);
  40                 } while(h2 != h);
  41
  42                 ret = (((u64)h) << 32) | l;
  43         } else
  44                 ret = READ_ONCE(*p);
  45
  46         return ret;
  47 }
  48
  49 /*
  50  * Runstate accounting
  51  */
  52 void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
  53 {
  54         u64 state_time;
  55         struct vcpu_runstate_info *state;
  56
  57         BUG_ON(preemptible());
  58
  59         state = this_cpu_ptr(&xen_runstate);
  60
  61         /*
  62          * The runstate info is always updated by the hypervisor on
  63          * the current CPU, so there's no need to use anything
  64          * stronger than a compiler barrier when fetching it.
  65          */
  66         do {
  67                 state_time = get64(&state->state_entry_time);
  68                 *res = READ_ONCE(*state);
  69         } while (get64(&state->state_entry_time) != state_time);
  70 }
  71
  72 /* return true when a vcpu could run but has no real cpu to run on */
  73 bool xen_vcpu_stolen(int vcpu)
  74 {
  75         return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
  76 }
  77
  78 void xen_setup_runstate_info(int cpu)
  79 {
  80         struct vcpu_register_runstate_memory_area area;
  81
  82         area.addr.v = &per_cpu(xen_runstate, cpu);
  83
  84         if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
  85                                cpu, &area))
  86                 BUG();
  87 }
  88