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
xen_parse_mc_debug(char * arg)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
mc_percpu_init(unsigned int cpu)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
mc_debug_enable(void)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
print_debug_data(struct mc_buffer * b,struct mc_debug_data * mcdb,int idx)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
xen_mc_flush(void)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
__xen_mc_entry(size_t args)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
xen_mc_extend_args(unsigned long op,size_t size)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
xen_mc_callback(void (* fn)(void *),void * data)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 }
298