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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