arch/x86/xen/multicalls.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Xen hypercall batching.
   4  *
   5  * Xen allows multiple hypercalls to be issued at once, using the
   6  * multicall interface.  This allows the cost of trapping into the
   7  * hypervisor to be amortized over several calls.
   8  *
   9  * This file implements a simple interface for multicalls.  There's a
  10  * per-cpu buffer of outstanding multicalls.  When you want to queue a
  11  * multicall for issuing, you can allocate a multicall slot for the
  12  * call and its arguments, along with storage for space which is
  13  * pointed to by the arguments (for passing pointers to structures,
  14  * etc).  When the multicall is actually issued, all the space for the
  15  * commands and allocated memory is freed for reuse.
  16  *
  17  * Multicalls are flushed whenever any of the buffers get full, or
  18  * when explicitly requested.  There's no way to get per-multicall
  19  * return results back.  It will BUG if any of the multicalls fail.
  20  *
  21  * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
  22  */
  23 #include <linux/percpu.h>
  24 #include <linux/hardirq.h>
  25 #include <linux/debugfs.h>
  26
  27 #include <asm/xen/hypercall.h>
  28
  29 #include "multicalls.h"
  30 #include "debugfs.h"
  31
  32 #define MC_BATCH        32
  33
  34 #define MC_DEBUG        0
  35
  36 #define MC_ARGS         (MC_BATCH * 16)
  37
  38
  39 struct mc_buffer {
  40         unsigned mcidx, argidx, cbidx;
  41         struct multicall_entry entries[MC_BATCH];
  42 #if MC_DEBUG
  43         struct multicall_entry debug[MC_BATCH];
  44         void *caller[MC_BATCH];
  45 #endif
  46         unsigned char args[MC_ARGS];
  47         struct callback {
  48                 void (*fn)(void *);
  49                 void *data;
  50         } callbacks[MC_BATCH];
  51 };
  52
  53 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
  54 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
  55
  56 void xen_mc_flush(void)
  57 {
  58         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
  59         struct multicall_entry *mc;
  60         int ret = 0;
  61         unsigned long flags;
  62         int i;
  63
  64         BUG_ON(preemptible());
  65
  66         /* Disable interrupts in case someone comes in and queues
  67            something in the middle */
  68         local_irq_save(flags);
  69
  70         trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
  71
  72 #if MC_DEBUG
  73         memcpy(b->debug, b->entries,
  74                b->mcidx * sizeof(struct multicall_entry));
  75 #endif
  76
  77         switch (b->mcidx) {
  78         case 0:
  79                 /* no-op */
  80                 BUG_ON(b->argidx != 0);
  81                 break;
  82
  83         case 1:
  84                 /* Singleton multicall - bypass multicall machinery
  85                    and just do the call directly. */
  86                 mc = &b->entries[0];
  87
  88                 mc->result = xen_single_call(mc->op, mc->args[0], mc->args[1],
  89                                              mc->args[2], mc->args[3],
  90                                              mc->args[4]);
  91                 ret = mc->result < 0;
  92                 break;
  93
  94         default:
  95                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
  96                         BUG();
  97                 for (i = 0; i < b->mcidx; i++)
  98                         if (b->entries[i].result < 0)
  99                                 ret++;
 100         }
 101
 102         if (WARN_ON(ret)) {
 103                 pr_err("%d of %d multicall(s) failed: cpu %d\n",
 104                        ret, b->mcidx, smp_processor_id());
 105                 for (i = 0; i < b->mcidx; i++) {
 106                         if (b->entries[i].result < 0) {
 107 #if MC_DEBUG
 108                                 pr_err("  call %2d: op=%lu arg=[%lx] result=%ld\t%pS\n",
 109                                        i + 1,
 110                                        b->debug[i].op,
 111                                        b->debug[i].args[0],
 112                                        b->entries[i].result,
 113                                        b->caller[i]);
 114 #else
 115                                 pr_err("  call %2d: op=%lu arg=[%lx] result=%ld\n",
 116                                        i + 1,
 117                                        b->entries[i].op,
 118                                        b->entries[i].args[0],
 119                                        b->entries[i].result);
 120 #endif
 121                         }
 122                 }
 123         }
 124
 125         b->mcidx = 0;
 126         b->argidx = 0;
 127
 128         for (i = 0; i < b->cbidx; i++) {
 129                 struct callback *cb = &b->callbacks[i];
 130
 131                 (*cb->fn)(cb->data);
 132         }
 133         b->cbidx = 0;
 134
 135         local_irq_restore(flags);
 136 }
 137
 138 struct multicall_space __xen_mc_entry(size_t args)
 139 {
 140         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 141         struct multicall_space ret;
 142         unsigned argidx = roundup(b->argidx, sizeof(u64));
 143
 144         trace_xen_mc_entry_alloc(args);
 145
 146         BUG_ON(preemptible());
 147         BUG_ON(b->argidx >= MC_ARGS);
 148
 149         if (unlikely(b->mcidx == MC_BATCH ||
 150                      (argidx + args) >= MC_ARGS)) {
 151                 trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ?
 152                                           XEN_MC_FL_BATCH : XEN_MC_FL_ARGS);
 153                 xen_mc_flush();
 154                 argidx = roundup(b->argidx, sizeof(u64));
 155         }
 156
 157         ret.mc = &b->entries[b->mcidx];
 158 #if MC_DEBUG
 159         b->caller[b->mcidx] = __builtin_return_address(0);
 160 #endif
 161         b->mcidx++;
 162         ret.args = &b->args[argidx];
 163         b->argidx = argidx + args;
 164
 165         BUG_ON(b->argidx >= MC_ARGS);
 166         return ret;
 167 }
 168
 169 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
 170 {
 171         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 172         struct multicall_space ret = { NULL, NULL };
 173
 174         BUG_ON(preemptible());
 175         BUG_ON(b->argidx >= MC_ARGS);
 176
 177         if (unlikely(b->mcidx == 0 ||
 178                      b->entries[b->mcidx - 1].op != op)) {
 179                 trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP);
 180                 goto out;
 181         }
 182
 183         if (unlikely((b->argidx + size) >= MC_ARGS)) {
 184                 trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE);
 185                 goto out;
 186         }
 187
 188         ret.mc = &b->entries[b->mcidx - 1];
 189         ret.args = &b->args[b->argidx];
 190         b->argidx += size;
 191
 192         BUG_ON(b->argidx >= MC_ARGS);
 193
 194         trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK);
 195 out:
 196         return ret;
 197 }
 198
 199 void xen_mc_callback(void (*fn)(void *), void *data)
 200 {
 201         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 202         struct callback *cb;
 203
 204         if (b->cbidx == MC_BATCH) {
 205                 trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
 206                 xen_mc_flush();
 207         }
 208
 209         trace_xen_mc_callback(fn, data);
 210
 211         cb = &b->callbacks[b->cbidx++];
 212         cb->fn = fn;
 213         cb->data = data;
 214 }