1 /*
2  * VMware VMCI Driver
3  *
4  * Copyright (C) 2012 VMware, Inc. All rights reserved.
5  *
6  * This program is free software; you can redistribute it and/or modify it
7  * under the terms of the GNU General Public License as published by the
8  * Free Software Foundation version 2 and no later version.
9  *
10  * This program is distributed in the hope that it will be useful, but
11  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
12  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13  * for more details.
14  */
15 
16 #include <linux/vmw_vmci_defs.h>
17 #include <linux/hash.h>
18 #include <linux/types.h>
19 #include <linux/rculist.h>
20 #include <linux/completion.h>
21 
22 #include "vmci_resource.h"
23 #include "vmci_driver.h"
24 
25 
26 #define VMCI_RESOURCE_HASH_BITS         7
27 #define VMCI_RESOURCE_HASH_BUCKETS      (1 << VMCI_RESOURCE_HASH_BITS)
28 
29 struct vmci_hash_table {
30 	spinlock_t lock;
31 	struct hlist_head entries[VMCI_RESOURCE_HASH_BUCKETS];
32 };
33 
34 static struct vmci_hash_table vmci_resource_table = {
35 	.lock = __SPIN_LOCK_UNLOCKED(vmci_resource_table.lock),
36 };
37 
38 static unsigned int vmci_resource_hash(struct vmci_handle handle)
39 {
40 	return hash_32(handle.resource, VMCI_RESOURCE_HASH_BITS);
41 }
42 
43 /*
44  * Gets a resource (if one exists) matching given handle from the hash table.
45  */
46 static struct vmci_resource *vmci_resource_lookup(struct vmci_handle handle,
47 						  enum vmci_resource_type type)
48 {
49 	struct vmci_resource *r, *resource = NULL;
50 	unsigned int idx = vmci_resource_hash(handle);
51 
52 	rcu_read_lock();
53 	hlist_for_each_entry_rcu(r,
54 				 &vmci_resource_table.entries[idx], node) {
55 		u32 cid = r->handle.context;
56 		u32 rid = r->handle.resource;
57 
58 		if (r->type == type &&
59 		    rid == handle.resource &&
60 		    (cid == handle.context || cid == VMCI_INVALID_ID)) {
61 			resource = r;
62 			break;
63 		}
64 	}
65 	rcu_read_unlock();
66 
67 	return resource;
68 }
69 
70 /*
71  * Find an unused resource ID and return it. The first
72  * VMCI_RESERVED_RESOURCE_ID_MAX are reserved so we start from
73  * its value + 1.
74  * Returns VMCI resource id on success, VMCI_INVALID_ID on failure.
75  */
76 static u32 vmci_resource_find_id(u32 context_id,
77 				 enum vmci_resource_type resource_type)
78 {
79 	static u32 resource_id = VMCI_RESERVED_RESOURCE_ID_MAX + 1;
80 	u32 old_rid = resource_id;
81 	u32 current_rid;
82 
83 	/*
84 	 * Generate a unique resource ID.  Keep on trying until we wrap around
85 	 * in the RID space.
86 	 */
87 	do {
88 		struct vmci_handle handle;
89 
90 		current_rid = resource_id;
91 		resource_id++;
92 		if (unlikely(resource_id == VMCI_INVALID_ID)) {
93 			/* Skip the reserved rids. */
94 			resource_id = VMCI_RESERVED_RESOURCE_ID_MAX + 1;
95 		}
96 
97 		handle = vmci_make_handle(context_id, current_rid);
98 		if (!vmci_resource_lookup(handle, resource_type))
99 			return current_rid;
100 	} while (resource_id != old_rid);
101 
102 	return VMCI_INVALID_ID;
103 }
104 
105 
106 int vmci_resource_add(struct vmci_resource *resource,
107 		      enum vmci_resource_type resource_type,
108 		      struct vmci_handle handle)
109 
110 {
111 	unsigned int idx;
112 	int result;
113 
114 	spin_lock(&vmci_resource_table.lock);
115 
116 	if (handle.resource == VMCI_INVALID_ID) {
117 		handle.resource = vmci_resource_find_id(handle.context,
118 			resource_type);
119 		if (handle.resource == VMCI_INVALID_ID) {
120 			result = VMCI_ERROR_NO_HANDLE;
121 			goto out;
122 		}
123 	} else if (vmci_resource_lookup(handle, resource_type)) {
124 		result = VMCI_ERROR_ALREADY_EXISTS;
125 		goto out;
126 	}
127 
128 	resource->handle = handle;
129 	resource->type = resource_type;
130 	INIT_HLIST_NODE(&resource->node);
131 	kref_init(&resource->kref);
132 	init_completion(&resource->done);
133 
134 	idx = vmci_resource_hash(resource->handle);
135 	hlist_add_head_rcu(&resource->node, &vmci_resource_table.entries[idx]);
136 
137 	result = VMCI_SUCCESS;
138 
139 out:
140 	spin_unlock(&vmci_resource_table.lock);
141 	return result;
142 }
143 
144 void vmci_resource_remove(struct vmci_resource *resource)
145 {
146 	struct vmci_handle handle = resource->handle;
147 	unsigned int idx = vmci_resource_hash(handle);
148 	struct vmci_resource *r;
149 
150 	/* Remove resource from hash table. */
151 	spin_lock(&vmci_resource_table.lock);
152 
153 	hlist_for_each_entry(r, &vmci_resource_table.entries[idx], node) {
154 		if (vmci_handle_is_equal(r->handle, resource->handle)) {
155 			hlist_del_init_rcu(&r->node);
156 			break;
157 		}
158 	}
159 
160 	spin_unlock(&vmci_resource_table.lock);
161 	synchronize_rcu();
162 
163 	vmci_resource_put(resource);
164 	wait_for_completion(&resource->done);
165 }
166 
167 struct vmci_resource *
168 vmci_resource_by_handle(struct vmci_handle resource_handle,
169 			enum vmci_resource_type resource_type)
170 {
171 	struct vmci_resource *r, *resource = NULL;
172 
173 	rcu_read_lock();
174 
175 	r = vmci_resource_lookup(resource_handle, resource_type);
176 	if (r &&
177 	    (resource_type == r->type ||
178 	     resource_type == VMCI_RESOURCE_TYPE_ANY)) {
179 		resource = vmci_resource_get(r);
180 	}
181 
182 	rcu_read_unlock();
183 
184 	return resource;
185 }
186 
187 /*
188  * Get a reference to given resource.
189  */
190 struct vmci_resource *vmci_resource_get(struct vmci_resource *resource)
191 {
192 	kref_get(&resource->kref);
193 
194 	return resource;
195 }
196 
197 static void vmci_release_resource(struct kref *kref)
198 {
199 	struct vmci_resource *resource =
200 		container_of(kref, struct vmci_resource, kref);
201 
202 	/* Verify the resource has been unlinked from hash table */
203 	WARN_ON(!hlist_unhashed(&resource->node));
204 
205 	/* Signal that container of this resource can now be destroyed */
206 	complete(&resource->done);
207 }
208 
209 /*
210  * Resource's release function will get called if last reference.
211  * If it is the last reference, then we are sure that nobody else
212  * can increment the count again (it's gone from the resource hash
213  * table), so there's no need for locking here.
214  */
215 int vmci_resource_put(struct vmci_resource *resource)
216 {
217 	/*
218 	 * We propagate the information back to caller in case it wants to know
219 	 * whether entry was freed.
220 	 */
221 	return kref_put(&resource->kref, vmci_release_resource) ?
222 		VMCI_SUCCESS_ENTRY_DEAD : VMCI_SUCCESS;
223 }
224 
225 struct vmci_handle vmci_resource_handle(struct vmci_resource *resource)
226 {
227 	return resource->handle;
228 }
229