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_BATCH        32
  30 #define MC_ARGS         (MC_BATCH * 16 / sizeof(u64))
  31
  32 struct mc_buffer {
  33         struct multicall_entry entries[MC_BATCH];
  34         u64 args[MC_ARGS];
  35         struct callback {
  36                 void (*fn)(void *);
  37                 void *data;
  38         } callbacks[MC_BATCH];
  39         unsigned mcidx, argidx, cbidx;
  40 };
  41
  42 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
  43 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
  44
  45 void xen_mc_flush(void)
  46 {
  47         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
  48         int ret = 0;
  49         unsigned long flags;
  50         int i;
  51
  52         BUG_ON(preemptible());
  53
  54         /* Disable interrupts in case someone comes in and queues
  55            something in the middle */
  56         local_irq_save(flags);
  57
  58         if (b->mcidx) {
  59                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
  60                         BUG();
  61                 for (i = 0; i < b->mcidx; i++)
  62                         if (b->entries[i].result < 0)
  63                                 ret++;
  64                 b->mcidx = 0;
  65                 b->argidx = 0;
  66         } else
  67                 BUG_ON(b->argidx != 0);
  68
  69         local_irq_restore(flags);
  70
  71         for(i = 0; i < b->cbidx; i++) {
  72                 struct callback *cb = &b->callbacks[i];
  73
  74                 (*cb->fn)(cb->data);
  75         }
  76         b->cbidx = 0;
  77
  78         BUG_ON(ret);
  79 }
  80
  81 struct multicall_space __xen_mc_entry(size_t args)
  82 {
  83         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
  84         struct multicall_space ret;
  85         unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
  86
  87         BUG_ON(preemptible());
  88         BUG_ON(argspace > MC_ARGS);
  89
  90         if (b->mcidx == MC_BATCH ||
  91             (b->argidx + argspace) > MC_ARGS)
  92                 xen_mc_flush();
  93
  94         ret.mc = &b->entries[b->mcidx];
  95         b->mcidx++;
  96         ret.args = &b->args[b->argidx];
  97         b->argidx += argspace;
  98
  99         return ret;
 100 }
 101
 102 void xen_mc_callback(void (*fn)(void *), void *data)
 103 {
 104         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 105         struct callback *cb;
 106
 107         if (b->cbidx == MC_BATCH)
 108                 xen_mc_flush();
 109
 110         cb = &b->callbacks[b->cbidx++];
 111         cb->fn = fn;
 112         cb->data = data;
 113 }