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
39struct 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
53static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
54DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
55
56void 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
138struct 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
169struct 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);
195out:
196	return ret;
197}
198
199void 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}
215