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
 38struct 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
 48struct 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
 55static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
 56static struct mc_debug_data mc_debug_data_early __initdata;
 57static struct mc_debug_data __percpu *mc_debug_data_ptr;
 58DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
 59
 60static struct static_key mc_debug __ro_after_init;
 61static bool mc_debug_enabled __initdata;
 62
 63static 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
 71static 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}
 78early_param("xen_mc_debug", xen_parse_mc_debug);
 79
 80static 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}
105early_initcall(mc_debug_enable);
106
107/* Number of parameters of hypercalls used via multicalls. */
108static 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
117static 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
142void 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
219struct 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
254struct 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);
280out:
281	return ret;
282}
283
284void 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}