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 
39 struct 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 
53 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
54 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
55 
xen_mc_flush(void)56 void 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 
__xen_mc_entry(size_t args)138 struct 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 
xen_mc_extend_args(unsigned long op,size_t size)169 struct 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);
195 out:
196 	return ret;
197 }
198 
xen_mc_callback(void (* fn)(void *),void * data)199 void 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