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 #include <linux/jump_label.h>
  27 #include <linux/printk.h>
  28
  29 #include <asm/xen/hypercall.h>
  30
  31 #include "xen-ops.h"
  32
  33 #define MC_BATCH        32
  34
  35 #define MC_ARGS         (MC_BATCH * 16)
  36
  37
  38 struct mc_buffer {
  39         unsigned mcidx, argidx, cbidx;
  40         struct multicall_entry entries[MC_BATCH];
  41         unsigned char args[MC_ARGS];
  42         struct callback {
  43                 void (*fn)(void *);
  44                 void *data;
  45         } callbacks[MC_BATCH];
  46 };
  47
  48 struct mc_debug_data {
  49         struct multicall_entry entries[MC_BATCH];
  50         void *caller[MC_BATCH];
  51         size_t argsz[MC_BATCH];
  52         unsigned long *args[MC_BATCH];
  53 };
  54
  55 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
  56 static struct mc_debug_data mc_debug_data_early __initdata;
  57 static DEFINE_PER_CPU(struct mc_debug_data *, mc_debug_data) =
  58         &mc_debug_data_early;
  59 static struct mc_debug_data __percpu *mc_debug_data_ptr;
  60 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
  61
  62 static struct static_key mc_debug __ro_after_init;
  63 static bool mc_debug_enabled __initdata;
  64
  65 static int __init xen_parse_mc_debug(char *arg)
  66 {
  67         mc_debug_enabled = true;
  68         static_key_slow_inc(&mc_debug);
  69
  70         return 0;
  71 }
  72 early_param("xen_mc_debug", xen_parse_mc_debug);
  73
  74 void mc_percpu_init(unsigned int cpu)
  75 {
  76         per_cpu(mc_debug_data, cpu) = per_cpu_ptr(mc_debug_data_ptr, cpu);
  77 }
  78
  79 static int __init mc_debug_enable(void)
  80 {
  81         unsigned long flags;
  82
  83         if (!mc_debug_enabled)
  84                 return 0;
  85
  86         mc_debug_data_ptr = alloc_percpu(struct mc_debug_data);
  87         if (!mc_debug_data_ptr) {
  88                 pr_err("xen_mc_debug inactive\n");
  89                 static_key_slow_dec(&mc_debug);
  90                 return -ENOMEM;
  91         }
  92
  93         /* Be careful when switching to percpu debug data. */
  94         local_irq_save(flags);
  95         xen_mc_flush();
  96         mc_percpu_init(0);
  97         local_irq_restore(flags);
  98
  99         pr_info("xen_mc_debug active\n");
 100
 101         return 0;
 102 }
 103 early_initcall(mc_debug_enable);
 104
 105 /* Number of parameters of hypercalls used via multicalls. */
 106 static const uint8_t hpcpars[] = {
 107         [__HYPERVISOR_mmu_update] = 4,
 108         [__HYPERVISOR_stack_switch] = 2,
 109         [__HYPERVISOR_fpu_taskswitch] = 1,
 110         [__HYPERVISOR_update_descriptor] = 2,
 111         [__HYPERVISOR_update_va_mapping] = 3,
 112         [__HYPERVISOR_mmuext_op] = 4,
 113 };
 114
 115 static void print_debug_data(struct mc_buffer *b, struct mc_debug_data *mcdb,
 116                              int idx)
 117 {
 118         unsigned int arg;
 119         unsigned int opidx = mcdb->entries[idx].op & 0xff;
 120         unsigned int pars = 0;
 121
 122         pr_err("  call %2d: op=%lu result=%ld caller=%pS ", idx + 1,
 123                mcdb->entries[idx].op, b->entries[idx].result,
 124                mcdb->caller[idx]);
 125         if (opidx < ARRAY_SIZE(hpcpars))
 126                 pars = hpcpars[opidx];
 127         if (pars) {
 128                 pr_cont("pars=");
 129                 for (arg = 0; arg < pars; arg++)
 130                         pr_cont("%lx ", mcdb->entries[idx].args[arg]);
 131         }
 132         if (mcdb->argsz[idx]) {
 133                 pr_cont("args=");
 134                 for (arg = 0; arg < mcdb->argsz[idx] / 8; arg++)
 135                         pr_cont("%lx ", mcdb->args[idx][arg]);
 136         }
 137         pr_cont("\n");
 138 }
 139
 140 void xen_mc_flush(void)
 141 {
 142         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 143         struct multicall_entry *mc;
 144         struct mc_debug_data *mcdb = NULL;
 145         int ret = 0;
 146         unsigned long flags;
 147         int i;
 148
 149         BUG_ON(preemptible());
 150
 151         /* Disable interrupts in case someone comes in and queues
 152            something in the middle */
 153         local_irq_save(flags);
 154
 155         trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
 156
 157         if (static_key_false(&mc_debug)) {
 158                 mcdb = __this_cpu_read(mc_debug_data);
 159                 memcpy(mcdb->entries, b->entries,
 160                        b->mcidx * sizeof(struct multicall_entry));
 161         }
 162
 163         switch (b->mcidx) {
 164         case 0:
 165                 /* no-op */
 166                 BUG_ON(b->argidx != 0);
 167                 break;
 168
 169         case 1:
 170                 /* Singleton multicall - bypass multicall machinery
 171                    and just do the call directly. */
 172                 mc = &b->entries[0];
 173
 174                 mc->result = xen_single_call(mc->op, mc->args[0], mc->args[1],
 175                                              mc->args[2], mc->args[3],
 176                                              mc->args[4]);
 177                 ret = mc->result < 0;
 178                 break;
 179
 180         default:
 181                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
 182                         BUG();
 183                 for (i = 0; i < b->mcidx; i++)
 184                         if (b->entries[i].result < 0)
 185                                 ret++;
 186         }
 187
 188         if (WARN_ON(ret)) {
 189                 pr_err("%d of %d multicall(s) failed: cpu %d\n",
 190                        ret, b->mcidx, smp_processor_id());
 191                 for (i = 0; i < b->mcidx; i++) {
 192                         if (static_key_false(&mc_debug)) {
 193                                 print_debug_data(b, mcdb, i);
 194                         } else if (b->entries[i].result < 0) {
 195                                 pr_err("  call %2d: op=%lu arg=[%lx] result=%ld\n",
 196                                        i + 1,
 197                                        b->entries[i].op,
 198                                        b->entries[i].args[0],
 199                                        b->entries[i].result);
 200                         }
 201                 }
 202         }
 203
 204         b->mcidx = 0;
 205         b->argidx = 0;
 206
 207         for (i = 0; i < b->cbidx; i++) {
 208                 struct callback *cb = &b->callbacks[i];
 209
 210                 (*cb->fn)(cb->data);
 211         }
 212         b->cbidx = 0;
 213
 214         local_irq_restore(flags);
 215 }
 216
 217 struct multicall_space __xen_mc_entry(size_t args)
 218 {
 219         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 220         struct multicall_space ret;
 221         unsigned argidx = roundup(b->argidx, sizeof(u64));
 222
 223         trace_xen_mc_entry_alloc(args);
 224
 225         BUG_ON(preemptible());
 226         BUG_ON(b->argidx >= MC_ARGS);
 227
 228         if (unlikely(b->mcidx == MC_BATCH ||
 229                      (argidx + args) >= MC_ARGS)) {
 230                 trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ?
 231                                           XEN_MC_FL_BATCH : XEN_MC_FL_ARGS);
 232                 xen_mc_flush();
 233                 argidx = roundup(b->argidx, sizeof(u64));
 234         }
 235
 236         ret.mc = &b->entries[b->mcidx];
 237         if (static_key_false(&mc_debug)) {
 238                 struct mc_debug_data *mcdb = __this_cpu_read(mc_debug_data);
 239
 240                 mcdb->caller[b->mcidx] = __builtin_return_address(0);
 241                 mcdb->argsz[b->mcidx] = args;
 242                 mcdb->args[b->mcidx] = (unsigned long *)(&b->args[argidx]);
 243         }
 244         b->mcidx++;
 245         ret.args = &b->args[argidx];
 246         b->argidx = argidx + args;
 247
 248         BUG_ON(b->argidx >= MC_ARGS);
 249         return ret;
 250 }
 251
 252 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
 253 {
 254         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 255         struct multicall_space ret = { NULL, NULL };
 256
 257         BUG_ON(preemptible());
 258         BUG_ON(b->argidx >= MC_ARGS);
 259
 260         if (unlikely(b->mcidx == 0 ||
 261                      b->entries[b->mcidx - 1].op != op)) {
 262                 trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP);
 263                 goto out;
 264         }
 265
 266         if (unlikely((b->argidx + size) >= MC_ARGS)) {
 267                 trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE);
 268                 goto out;
 269         }
 270
 271         ret.mc = &b->entries[b->mcidx - 1];
 272         ret.args = &b->args[b->argidx];
 273         b->argidx += size;
 274
 275         BUG_ON(b->argidx >= MC_ARGS);
 276
 277         trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK);
 278 out:
 279         return ret;
 280 }
 281
 282 void xen_mc_callback(void (*fn)(void *), void *data)
 283 {
 284         struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
 285         struct callback *cb;
 286
 287         if (b->cbidx == MC_BATCH) {
 288                 trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
 289                 xen_mc_flush();
 290         }
 291
 292         trace_xen_mc_callback(fn, data);
 293
 294         cb = &b->callbacks[b->cbidx++];
 295         cb->fn = fn;
 296         cb->data = data;
 297 }