multicalls.c revision eac303bf2ef63e7f7b6971badea0ff7bf08a2b22 
1/*
2 * Xen hypercall batching.
3 *
4 * Xen allows multiple hypercalls to be issued at once, using the
5 * multicall interface.  This allows the cost of trapping into the
6 * hypervisor to be amortized over several calls.
7 *
8 * This file implements a simple interface for multicalls.  There's a
9 * per-cpu buffer of outstanding multicalls.  When you want to queue a
10 * multicall for issuing, you can allocate a multicall slot for the
11 * call and its arguments, along with storage for space which is
12 * pointed to by the arguments (for passing pointers to structures,
13 * etc).  When the multicall is actually issued, all the space for the
14 * commands and allocated memory is freed for reuse.
15 *
16 * Multicalls are flushed whenever any of the buffers get full, or
17 * when explicitly requested.  There's no way to get per-multicall
18 * return results back.  It will BUG if any of the multicalls fail.
19 *
20 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
21 */
22#include <linux/percpu.h>
23#include <linux/hardirq.h>
24#include <linux/debugfs.h>
25
26#include <asm/xen/hypercall.h>
27
28#include "multicalls.h"
29#include "debugfs.h"
30
31#define MC_BATCH	32
32
33#define MC_DEBUG	0
34
35#define MC_ARGS		(MC_BATCH * 16)
36
37
38struct mc_buffer {
39	struct multicall_entry entries[MC_BATCH];
40#if MC_DEBUG
41	struct multicall_entry debug[MC_BATCH];
42	void *caller[MC_BATCH];
43#endif
44	unsigned char args[MC_ARGS];
45	struct callback {
46		void (*fn)(void *);
47		void *data;
48	} callbacks[MC_BATCH];
49	unsigned mcidx, argidx, cbidx;
50};
51
52static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
53DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
54
55void xen_mc_flush(void)
56{
57	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
58	struct multicall_entry *mc;
59	int ret = 0;
60	unsigned long flags;
61	int i;
62
63	BUG_ON(preemptible());
64
65	/* Disable interrupts in case someone comes in and queues
66	   something in the middle */
67	local_irq_save(flags);
68
69	trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
70
71	switch (b->mcidx) {
72	case 0:
73		/* no-op */
74		BUG_ON(b->argidx != 0);
75		break;
76
77	case 1:
78		/* Singleton multicall - bypass multicall machinery
79		   and just do the call directly. */
80		mc = &b->entries[0];
81
82		mc->result = privcmd_call(mc->op,
83					  mc->args[0], mc->args[1], mc->args[2],
84					  mc->args[3], mc->args[4]);
85		ret = mc->result < 0;
86		break;
87
88	default:
89#if MC_DEBUG
90		memcpy(b->debug, b->entries,
91		       b->mcidx * sizeof(struct multicall_entry));
92#endif
93
94		if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
95			BUG();
96		for (i = 0; i < b->mcidx; i++)
97			if (b->entries[i].result < 0)
98				ret++;
99
100#if MC_DEBUG
101		if (ret) {
102			printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
103			       ret, smp_processor_id());
104			dump_stack();
105			for (i = 0; i < b->mcidx; i++) {
106				printk(KERN_DEBUG "  call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
107				       i+1, b->mcidx,
108				       b->debug[i].op,
109				       b->debug[i].args[0],
110				       b->entries[i].result,
111				       b->caller[i]);
112			}
113		}
114#endif
115	}
116
117	b->mcidx = 0;
118	b->argidx = 0;
119
120	for (i = 0; i < b->cbidx; i++) {
121		struct callback *cb = &b->callbacks[i];
122
123		(*cb->fn)(cb->data);
124	}
125	b->cbidx = 0;
126
127	local_irq_restore(flags);
128
129	WARN_ON(ret);
130}
131
132struct multicall_space __xen_mc_entry(size_t args)
133{
134	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
135	struct multicall_space ret;
136	unsigned argidx = roundup(b->argidx, sizeof(u64));
137
138	trace_xen_mc_entry_alloc(args);
139
140	BUG_ON(preemptible());
141	BUG_ON(b->argidx >= MC_ARGS);
142
143	if (unlikely(b->mcidx == MC_BATCH ||
144		     (argidx + args) >= MC_ARGS)) {
145		trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ?
146					  XEN_MC_FL_BATCH : XEN_MC_FL_ARGS);
147		xen_mc_flush();
148		argidx = roundup(b->argidx, sizeof(u64));
149	}
150
151	ret.mc = &b->entries[b->mcidx];
152#if MC_DEBUG
153	b->caller[b->mcidx] = __builtin_return_address(0);
154#endif
155	b->mcidx++;
156	ret.args = &b->args[argidx];
157	b->argidx = argidx + args;
158
159	BUG_ON(b->argidx >= MC_ARGS);
160	return ret;
161}
162
163struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
164{
165	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
166	struct multicall_space ret = { NULL, NULL };
167
168	BUG_ON(preemptible());
169	BUG_ON(b->argidx >= MC_ARGS);
170
171	if (unlikely(b->mcidx == 0 ||
172		     b->entries[b->mcidx - 1].op != op)) {
173		trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP);
174		goto out;
175	}
176
177	if (unlikely((b->argidx + size) >= MC_ARGS)) {
178		trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE);
179		goto out;
180	}
181
182	ret.mc = &b->entries[b->mcidx - 1];
183	ret.args = &b->args[b->argidx];
184	b->argidx += size;
185
186	BUG_ON(b->argidx >= MC_ARGS);
187
188	trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK);
189out:
190	return ret;
191}
192
193void xen_mc_callback(void (*fn)(void *), void *data)
194{
195	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
196	struct callback *cb;
197
198	if (b->cbidx == MC_BATCH) {
199		trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
200		xen_mc_flush();
201	}
202
203	trace_xen_mc_callback(fn, data);
204
205	cb = &b->callbacks[b->cbidx++];
206	cb->fn = fn;
207	cb->data = data;
208}
209