xref: /openbmc/linux/arch/x86/xen/multicalls.c (revision 22246614)
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 
25 #include <asm/xen/hypercall.h>
26 
27 #include "multicalls.h"
28 
29 #define MC_DEBUG	1
30 
31 #define MC_BATCH	32
32 #define MC_ARGS		(MC_BATCH * 16 / sizeof(u64))
33 
34 struct mc_buffer {
35 	struct multicall_entry entries[MC_BATCH];
36 #if MC_DEBUG
37 	struct multicall_entry debug[MC_BATCH];
38 #endif
39 	u64 args[MC_ARGS];
40 	struct callback {
41 		void (*fn)(void *);
42 		void *data;
43 	} callbacks[MC_BATCH];
44 	unsigned mcidx, argidx, cbidx;
45 };
46 
47 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
48 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
49 
50 void xen_mc_flush(void)
51 {
52 	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
53 	int ret = 0;
54 	unsigned long flags;
55 	int i;
56 
57 	BUG_ON(preemptible());
58 
59 	/* Disable interrupts in case someone comes in and queues
60 	   something in the middle */
61 	local_irq_save(flags);
62 
63 	if (b->mcidx) {
64 #if MC_DEBUG
65 		memcpy(b->debug, b->entries,
66 		       b->mcidx * sizeof(struct multicall_entry));
67 #endif
68 
69 		if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
70 			BUG();
71 		for (i = 0; i < b->mcidx; i++)
72 			if (b->entries[i].result < 0)
73 				ret++;
74 
75 #if MC_DEBUG
76 		if (ret) {
77 			printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
78 			       ret, smp_processor_id());
79 			for (i = 0; i < b->mcidx; i++) {
80 				printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
81 				       i+1, b->mcidx,
82 				       b->debug[i].op,
83 				       b->debug[i].args[0],
84 				       b->entries[i].result);
85 			}
86 		}
87 #endif
88 
89 		b->mcidx = 0;
90 		b->argidx = 0;
91 	} else
92 		BUG_ON(b->argidx != 0);
93 
94 	local_irq_restore(flags);
95 
96 	for (i = 0; i < b->cbidx; i++) {
97 		struct callback *cb = &b->callbacks[i];
98 
99 		(*cb->fn)(cb->data);
100 	}
101 	b->cbidx = 0;
102 
103 	BUG_ON(ret);
104 }
105 
106 struct multicall_space __xen_mc_entry(size_t args)
107 {
108 	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
109 	struct multicall_space ret;
110 	unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
111 
112 	BUG_ON(preemptible());
113 	BUG_ON(argspace > MC_ARGS);
114 
115 	if (b->mcidx == MC_BATCH ||
116 	    (b->argidx + argspace) > MC_ARGS)
117 		xen_mc_flush();
118 
119 	ret.mc = &b->entries[b->mcidx];
120 	b->mcidx++;
121 	ret.args = &b->args[b->argidx];
122 	b->argidx += argspace;
123 
124 	return ret;
125 }
126 
127 void xen_mc_callback(void (*fn)(void *), void *data)
128 {
129 	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
130 	struct callback *cb;
131 
132 	if (b->cbidx == MC_BATCH)
133 		xen_mc_flush();
134 
135 	cb = &b->callbacks[b->cbidx++];
136 	cb->fn = fn;
137 	cb->data = data;
138 }
139