arch/x86/xen/multicalls.c

   1 /*
   2  * Xen hypercall batching.
   3  *
   4  * Xen allows multiple hypercalls to be issued at once, using the
   5  * multicall interface.  This allows the cost of trapping into the
   6  * hypervisor to be amortized over several calls.
   7  *
   8  * This file implements a simple interface for multicalls.  There's a
   9  * per-cpu buffer of outstanding multicalls.  When you want to queue a
  10  * multicall for issuing, you can allocate a multicall slot for the
  11  * call and its arguments, along with storage for space which is
  12  * pointed to by the arguments (for passing pointers to structures,
  13  * etc).  When the multicall is actually issued, all the space for the
  14  * commands and allocated memory is freed for reuse.
  15  *
  16  * Multicalls are flushed whenever any of the buffers get full, or
  17  * when explicitly requested.  There's no way to get per-multicall
  18  * return results back.  It will BUG if any of the multicalls fail.
  19  *
  20  * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
  21  */
  22 #include <linux/percpu.h>
  23 #include <linux/hardirq.h>
  24
  25 #include <asm/xen/hypercall.h>
  26
  27 #include "multicalls.h"
  28
  29 #define MC_DEBUG        1
  30
  31 #define MC_BATCH        32
  32 #define MC_ARGS         (MC_BATCH * 16)
  33
  34 struct mc_buffer {
  35         struct multicall_entry entries[MC_BATCH];
  36 #if MC_DEBUG
  37         struct multicall_entry debug[MC_BATCH];
  38 #endif
  39         unsigned char args[MC_ARGS];
  40         struct callback {
  41                 void (*fn)(void *);
  42                 void *data;
  43         } callbacks[MC_BATCH];
  44         unsigned mcidx, argidx, cbidx;
  45 };
  46
  47 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
  48 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
  49
  50 void xen_mc_flush(void)
  51 {
  52         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
  53         int ret = 0;
  54         unsigned long flags;
  55         int i;
  56
  57         BUG_ON(preemptible());
  58
  59         /* Disable interrupts in case someone comes in and queues
  60            something in the middle */
  61         local_irq_save(flags);
  62
  63         if (b->mcidx) {
  64 #if MC_DEBUG
  65                 memcpy(b->debug, b->entries,
  66                        b->mcidx * sizeof(struct multicall_entry));
  67 #endif
  68
  69                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
  70                         BUG();
  71                 for (i = 0; i < b->mcidx; i++)
  72                         if (b->entries[i].result < 0)
  73                                 ret++;
  74
  75 #if MC_DEBUG
  76                 if (ret) {
  77                         printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
  78                                ret, smp_processor_id());
  79                         dump_stack();
  80                         for (i = 0; i < b->mcidx; i++) {
  81                                 printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
  82                                        i+1, b->mcidx,
  83                                        b->debug[i].op,
  84                                        b->debug[i].args[0],
  85                                        b->entries[i].result);
  86                         }
  87                 }
  88 #endif
  89
  90                 b->mcidx = 0;
  91                 b->argidx = 0;
  92         } else
  93                 BUG_ON(b->argidx != 0);
  94
  95         local_irq_restore(flags);
  96
  97         for (i = 0; i < b->cbidx; i++) {
  98                 struct callback *cb = &b->callbacks[i];
  99
 100                 (*cb->fn)(cb->data);
 101         }
 102         b->cbidx = 0;
 103
 104         BUG_ON(ret);
 105 }
 106
 107 struct multicall_space __xen_mc_entry(size_t args)
 108 {
 109         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 110         struct multicall_space ret;
 111         unsigned argidx = roundup(b->argidx, sizeof(u64));
 112
 113         BUG_ON(preemptible());
 114         BUG_ON(b->argidx > MC_ARGS);
 115
 116         if (b->mcidx == MC_BATCH ||
 117             (argidx + args) > MC_ARGS) {
 118                 xen_mc_flush();
 119                 argidx = roundup(b->argidx, sizeof(u64));
 120         }
 121
 122         ret.mc = &b->entries[b->mcidx];
 123         b->mcidx++;
 124         ret.args = &b->args[argidx];
 125         b->argidx = argidx + args;
 126
 127         BUG_ON(b->argidx > MC_ARGS);
 128         return ret;
 129 }
 130
 131 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
 132 {
 133         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 134         struct multicall_space ret = { NULL, NULL };
 135
 136         BUG_ON(preemptible());
 137         BUG_ON(b->argidx > MC_ARGS);
 138
 139         if (b->mcidx == 0)
 140                 return ret;
 141
 142         if (b->entries[b->mcidx - 1].op != op)
 143                 return ret;
 144
 145         if ((b->argidx + size) > MC_ARGS)
 146                 return ret;
 147
 148         ret.mc = &b->entries[b->mcidx - 1];
 149         ret.args = &b->args[b->argidx];
 150         b->argidx += size;
 151
 152         BUG_ON(b->argidx > MC_ARGS);
 153         return ret;
 154 }
 155
 156 void xen_mc_callback(void (*fn)(void *), void *data)
 157 {
 158         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 159         struct callback *cb;
 160
 161         if (b->cbidx == MC_BATCH)
 162                 xen_mc_flush();
 163
 164         cb = &b->callbacks[b->cbidx++];
 165         cb->fn = fn;
 166         cb->data = data;
 167 }