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
38 struct mc_buffer {
39 unsigned mcidx, argidx, cbidx;
40 struct multicall_entry entries[MC_BATCH];
41 #if MC_DEBUG
42 struct multicall_entry debug[MC_BATCH];
43 void *caller[MC_BATCH];
44 #endif
45 unsigned char args[MC_ARGS];
46 struct callback {
47 void (*fn)(void *);
48 void *data;
49 } callbacks[MC_BATCH];
50 };
51
52 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
53 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
54
xen_mc_flush(void)55 void xen_mc_flush(void)
56 {
57 struct mc_buffer *b = this_cpu_ptr(&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
__xen_mc_entry(size_t args)132 struct multicall_space __xen_mc_entry(size_t args)
133 {
134 struct mc_buffer *b = this_cpu_ptr(&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
xen_mc_extend_args(unsigned long op,size_t size)163 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
164 {
165 struct mc_buffer *b = this_cpu_ptr(&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);
189 out:
190 return ret;
191 }
192
xen_mc_callback(void (* fn)(void *),void * data)193 void xen_mc_callback(void (*fn)(void *), void *data)
194 {
195 struct mc_buffer *b = this_cpu_ptr(&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