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 / sizeof(u64))
  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         u64 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                         for (i = 0; i < b->mcidx; i++) {
  80                                 printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
  81                                        i+1, b->mcidx,
  82                                        b->debug[i].op,
  83                                        b->debug[i].args[0],
  84                                        b->entries[i].result);
  85                         }
  86                 }
  87 #endif
  88
  89                 b->mcidx = 0;
  90                 b->argidx = 0;
  91         } else
  92                 BUG_ON(b->argidx != 0);
  93
  94         local_irq_restore(flags);
  95
  96         for (i = 0; i < b->cbidx; i++) {
  97                 struct callback *cb = &b->callbacks[i];
  98
  99                 (*cb->fn)(cb->data);
 100         }
 101         b->cbidx = 0;
 102
 103         BUG_ON(ret);
 104 }
 105
 106 struct multicall_space __xen_mc_entry(size_t args)
 107 {
 108         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 109         struct multicall_space ret;
 110         unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
 111
 112         BUG_ON(preemptible());
 113         BUG_ON(argspace > MC_ARGS);
 114
 115         if (b->mcidx == MC_BATCH ||
 116             (b->argidx + argspace) > MC_ARGS)
 117                 xen_mc_flush();
 118
 119         ret.mc = &b->entries[b->mcidx];
 120         b->mcidx++;
 121         ret.args = &b->args[b->argidx];
 122         b->argidx += argspace;
 123
 124         return ret;
 125 }
 126
 127 void xen_mc_callback(void (*fn)(void *), void *data)
 128 {
 129         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 130         struct callback *cb;
 131
 132         if (b->cbidx == MC_BATCH)
 133                 xen_mc_flush();
 134
 135         cb = &b->callbacks[b->cbidx++];
 136         cb->fn = fn;
 137         cb->data = data;
 138 }