1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright Rusty Russell IBM Corporation 2007.
5 *
6 * This header is BSD licensed so anyone can use the definitions to implement
7 * compatible drivers/servers.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of IBM nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33 #ifndef VIRTIO_RING_H
34 #define VIRTIO_RING_H
35
36 /* This marks a buffer as continuing via the next field. */
37 #define VRING_DESC_F_NEXT 1
38 /* This marks a buffer as write-only (otherwise read-only). */
39 #define VRING_DESC_F_WRITE 2
40 /* This means the buffer contains a list of buffer descriptors. */
41 #define VRING_DESC_F_INDIRECT 4
42
43 /* The Host uses this in used->flags to advise the Guest: don't kick me
44 * when you add a buffer. It's unreliable, so it's simply an
45 * optimization. Guest will still kick if it's out of buffers. */
46 #define VRING_USED_F_NO_NOTIFY 1
47 /* The Guest uses this in avail->flags to advise the Host: don't
48 * interrupt me when you consume a buffer. It's unreliable, so it's
49 * simply an optimization. */
50 #define VRING_AVAIL_F_NO_INTERRUPT 1
51
52 /* VirtIO ring descriptors: 16 bytes.
53 * These can chain together via "next". */
54 struct vring_desc {
55 /* Address (guest-physical). */
56 uint64_t addr;
57 /* Length. */
58 uint32_t len;
59 /* The flags as indicated above. */
60 uint16_t flags;
61 /* We chain unused descriptors via this, too. */
62 uint16_t next;
63 };
64
65 struct vring_avail {
66 uint16_t flags;
67 uint16_t idx;
68 uint16_t ring[0];
69 };
70
71 /* uint32_t is used here for ids for padding reasons. */
72 struct vring_used_elem {
73 /* Index of start of used descriptor chain. */
74 uint32_t id;
75 /* Total length of the descriptor chain which was written to. */
76 uint32_t len;
77 };
78
79 struct vring_used {
80 uint16_t flags;
81 uint16_t idx;
82 struct vring_used_elem ring[0];
83 };
84
85 struct vring {
86 unsigned int num;
87
88 struct vring_desc *desc;
89 struct vring_avail *avail;
90 struct vring_used *used;
91
92 vm_paddr_t desc_paddr;
93 vm_paddr_t avail_paddr;
94 vm_paddr_t used_paddr;
95 };
96
97 /* Alignment requirements for vring elements.
98 * When using pre-virtio 1.0 layout, these fall out naturally.
99 */
100 #define VRING_AVAIL_ALIGN_SIZE 2
101 #define VRING_USED_ALIGN_SIZE 4
102 #define VRING_DESC_ALIGN_SIZE 16
103
104 /* The standard layout for the ring is a continuous chunk of memory which
105 * looks like this. We assume num is a power of 2.
106 *
107 * struct vring {
108 * // The actual descriptors (16 bytes each)
109 * struct vring_desc desc[num];
110 *
111 * // A ring of available descriptor heads with free-running index.
112 * __u16 avail_flags;
113 * __u16 avail_idx;
114 * __u16 available[num];
115 * __u16 used_event_idx;
116 *
117 * // Padding to the next align boundary.
118 * char pad[];
119 *
120 * // A ring of used descriptor heads with free-running index.
121 * __u16 used_flags;
122 * __u16 used_idx;
123 * struct vring_used_elem used[num];
124 * __u16 avail_event_idx;
125 * };
126 *
127 * NOTE: for VirtIO PCI, align is 4096.
128 */
129
130 /*
131 * We publish the used event index at the end of the available ring, and vice
132 * versa. They are at the end for backwards compatibility.
133 */
134 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
135 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
136
137 static inline int
vring_size(unsigned int num,unsigned long align)138 vring_size(unsigned int num, unsigned long align)
139 {
140 int size;
141
142 size = num * sizeof(struct vring_desc);
143 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) +
144 sizeof(uint16_t);
145 size = (size + align - 1) & ~(align - 1);
146 size += sizeof(struct vring_used) +
147 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
148 return (size);
149 }
150
151 static inline void
vring_init(struct vring * vr,unsigned int num,uint8_t * p,vm_paddr_t paddr,unsigned long align)152 vring_init(struct vring *vr, unsigned int num, uint8_t *p, vm_paddr_t paddr,
153 unsigned long align)
154 {
155 unsigned long avail_offset;
156 unsigned long used_offset;
157
158 avail_offset = num * sizeof(struct vring_desc);
159 used_offset = (avail_offset + sizeof(struct vring_avail) +
160 sizeof(uint16_t) * num + align - 1) & ~(align - 1);
161
162 vr->num = num;
163 vr->desc = (struct vring_desc *) p;
164 vr->avail = (struct vring_avail *) (p + avail_offset);
165 vr->used = (struct vring_used *) (p + used_offset);
166
167 vr->desc_paddr = paddr;
168 vr->avail_paddr = paddr + avail_offset;
169 vr->used_paddr = paddr + used_offset;
170 }
171
172 /*
173 * The following is used with VIRTIO_RING_F_EVENT_IDX.
174 *
175 * Assuming a given event_idx value from the other size, if we have
176 * just incremented index from old to new_idx, should we trigger an
177 * event?
178 */
179 static inline int
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)180 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
181 {
182
183 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
184 }
185 #endif /* VIRTIO_RING_H */
186