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 struct mc_debug_data __percpu *mc_debug_data_ptr; 58 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags); 59 60 static struct static_key mc_debug __ro_after_init; 61 static bool mc_debug_enabled __initdata; 62 63 static struct mc_debug_data * __ref get_mc_debug(void) 64 { 65 if (!mc_debug_data_ptr) 66 return &mc_debug_data_early; 67 68 return this_cpu_ptr(mc_debug_data_ptr); 69 } 70 71 static int __init xen_parse_mc_debug(char *arg) 72 { 73 mc_debug_enabled = true; 74 static_key_slow_inc(&mc_debug); 75 76 return 0; 77 } 78 early_param("xen_mc_debug", xen_parse_mc_debug); 79 80 static int __init mc_debug_enable(void) 81 { 82 unsigned long flags; 83 struct mc_debug_data __percpu *mcdb; 84 85 if (!mc_debug_enabled) 86 return 0; 87 88 mcdb = alloc_percpu(struct mc_debug_data); 89 if (!mcdb) { 90 pr_err("xen_mc_debug inactive\n"); 91 static_key_slow_dec(&mc_debug); 92 return -ENOMEM; 93 } 94 95 /* Be careful when switching to percpu debug data. */ 96 local_irq_save(flags); 97 xen_mc_flush(); 98 mc_debug_data_ptr = mcdb; 99 local_irq_restore(flags); 100 101 pr_info("xen_mc_debug active\n"); 102 103 return 0; 104 } 105 early_initcall(mc_debug_enable); 106 107 /* Number of parameters of hypercalls used via multicalls. */ 108 static const uint8_t hpcpars[] = { 109 [__HYPERVISOR_mmu_update] = 4, 110 [__HYPERVISOR_stack_switch] = 2, 111 [__HYPERVISOR_fpu_taskswitch] = 1, 112 [__HYPERVISOR_update_descriptor] = 2, 113 [__HYPERVISOR_update_va_mapping] = 3, 114 [__HYPERVISOR_mmuext_op] = 4, 115 }; 116 117 static void print_debug_data(struct mc_buffer *b, struct mc_debug_data *mcdb, 118 int idx) 119 { 120 unsigned int arg; 121 unsigned int opidx = mcdb->entries[idx].op & 0xff; 122 unsigned int pars = 0; 123 124 pr_err(" call %2d: op=%lu result=%ld caller=%pS ", idx + 1, 125 mcdb->entries[idx].op, b->entries[idx].result, 126 mcdb->caller[idx]); 127 if (opidx < ARRAY_SIZE(hpcpars)) 128 pars = hpcpars[opidx]; 129 if (pars) { 130 pr_cont("pars="); 131 for (arg = 0; arg < pars; arg++) 132 pr_cont("%lx ", mcdb->entries[idx].args[arg]); 133 } 134 if (mcdb->argsz[idx]) { 135 pr_cont("args="); 136 for (arg = 0; arg < mcdb->argsz[idx] / 8; arg++) 137 pr_cont("%lx ", mcdb->args[idx][arg]); 138 } 139 pr_cont("\n"); 140 } 141 142 void xen_mc_flush(void) 143 { 144 struct mc_buffer *b = this_cpu_ptr(&mc_buffer); 145 struct multicall_entry *mc; 146 struct mc_debug_data *mcdb = NULL; 147 int ret = 0; 148 unsigned long flags; 149 int i; 150 151 BUG_ON(preemptible()); 152 153 /* Disable interrupts in case someone comes in and queues 154 something in the middle */ 155 local_irq_save(flags); 156 157 trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx); 158 159 if (static_key_false(&mc_debug)) { 160 mcdb = get_mc_debug(); 161 memcpy(mcdb->entries, b->entries, 162 b->mcidx * sizeof(struct multicall_entry)); 163 } 164 165 switch (b->mcidx) { 166 case 0: 167 /* no-op */ 168 BUG_ON(b->argidx != 0); 169 break; 170 171 case 1: 172 /* Singleton multicall - bypass multicall machinery 173 and just do the call directly. */ 174 mc = &b->entries[0]; 175 176 mc->result = xen_single_call(mc->op, mc->args[0], mc->args[1], 177 mc->args[2], mc->args[3], 178 mc->args[4]); 179 ret = mc->result < 0; 180 break; 181 182 default: 183 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0) 184 BUG(); 185 for (i = 0; i < b->mcidx; i++) 186 if (b->entries[i].result < 0) 187 ret++; 188 } 189 190 if (WARN_ON(ret)) { 191 pr_err("%d of %d multicall(s) failed: cpu %d\n", 192 ret, b->mcidx, smp_processor_id()); 193 for (i = 0; i < b->mcidx; i++) { 194 if (static_key_false(&mc_debug)) { 195 print_debug_data(b, mcdb, i); 196 } else if (b->entries[i].result < 0) { 197 pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\n", 198 i + 1, 199 b->entries[i].op, 200 b->entries[i].args[0], 201 b->entries[i].result); 202 } 203 } 204 } 205 206 b->mcidx = 0; 207 b->argidx = 0; 208 209 for (i = 0; i < b->cbidx; i++) { 210 struct callback *cb = &b->callbacks[i]; 211 212 (*cb->fn)(cb->data); 213 } 214 b->cbidx = 0; 215 216 local_irq_restore(flags); 217 } 218 219 struct multicall_space __xen_mc_entry(size_t args) 220 { 221 struct mc_buffer *b = this_cpu_ptr(&mc_buffer); 222 struct multicall_space ret; 223 unsigned argidx = roundup(b->argidx, sizeof(u64)); 224 225 trace_xen_mc_entry_alloc(args); 226 227 BUG_ON(preemptible()); 228 BUG_ON(b->argidx >= MC_ARGS); 229 230 if (unlikely(b->mcidx == MC_BATCH || 231 (argidx + args) >= MC_ARGS)) { 232 trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ? 233 XEN_MC_FL_BATCH : XEN_MC_FL_ARGS); 234 xen_mc_flush(); 235 argidx = roundup(b->argidx, sizeof(u64)); 236 } 237 238 ret.mc = &b->entries[b->mcidx]; 239 if (static_key_false(&mc_debug)) { 240 struct mc_debug_data *mcdb = get_mc_debug(); 241 242 mcdb->caller[b->mcidx] = __builtin_return_address(0); 243 mcdb->argsz[b->mcidx] = args; 244 mcdb->args[b->mcidx] = (unsigned long *)(&b->args[argidx]); 245 } 246 b->mcidx++; 247 ret.args = &b->args[argidx]; 248 b->argidx = argidx + args; 249 250 BUG_ON(b->argidx >= MC_ARGS); 251 return ret; 252 } 253 254 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size) 255 { 256 struct mc_buffer *b = this_cpu_ptr(&mc_buffer); 257 struct multicall_space ret = { NULL, NULL }; 258 259 BUG_ON(preemptible()); 260 BUG_ON(b->argidx >= MC_ARGS); 261 262 if (unlikely(b->mcidx == 0 || 263 b->entries[b->mcidx - 1].op != op)) { 264 trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP); 265 goto out; 266 } 267 268 if (unlikely((b->argidx + size) >= MC_ARGS)) { 269 trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE); 270 goto out; 271 } 272 273 ret.mc = &b->entries[b->mcidx - 1]; 274 ret.args = &b->args[b->argidx]; 275 b->argidx += size; 276 277 BUG_ON(b->argidx >= MC_ARGS); 278 279 trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK); 280 out: 281 return ret; 282 } 283 284 void xen_mc_callback(void (*fn)(void *), void *data) 285 { 286 struct mc_buffer *b = this_cpu_ptr(&mc_buffer); 287 struct callback *cb; 288 289 if (b->cbidx == MC_BATCH) { 290 trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK); 291 xen_mc_flush(); 292 } 293 294 trace_xen_mc_callback(fn, data); 295 296 cb = &b->callbacks[b->cbidx++]; 297 cb->fn = fn; 298 cb->data = data; 299 } 300