1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2016 Red Hat, Inc.
4 * Author: Michael S. Tsirkin <mst@redhat.com>
5 *
6 * Partial implementation of virtio 0.9. event index is used for signalling,
7 * unconditionally. Design roughly follows linux kernel implementation in order
8 * to be able to judge its performance.
9 */
10#define _GNU_SOURCE
11#include "main.h"
12#include <stdlib.h>
13#include <stdio.h>
14#include <assert.h>
15#include <string.h>
16#include <linux/virtio_ring.h>
17
18struct data {
19 void *data;
20} *data;
21
22struct vring ring;
23
24/* enabling the below activates experimental ring polling code
25 * (which skips index reads on consumer in favor of looking at
26 * high bits of ring id ^ 0x8000).
27 */
28/* #ifdef RING_POLL */
29/* enabling the below activates experimental in-order code
30 * (which skips ring updates and reads and writes len in descriptor).
31 */
32/* #ifdef INORDER */
33
34#if defined(RING_POLL) && defined(INORDER)
35#error "RING_POLL and INORDER are mutually exclusive"
36#endif
37
38/* how much padding is needed to avoid false cache sharing */
39#define HOST_GUEST_PADDING 0x80
40
41struct guest {
42 unsigned short avail_idx;
43 unsigned short last_used_idx;
44 unsigned short num_free;
45 unsigned short kicked_avail_idx;
46#ifndef INORDER
47 unsigned short free_head;
48#else
49 unsigned short reserved_free_head;
50#endif
51 unsigned char reserved[HOST_GUEST_PADDING - 10];
52} guest;
53
54struct host {
55 /* we do not need to track last avail index
56 * unless we have more than one in flight.
57 */
58 unsigned short used_idx;
59 unsigned short called_used_idx;
60 unsigned char reserved[HOST_GUEST_PADDING - 4];
61} host;
62
63/* implemented by ring */
64void alloc_ring(void)
65{
66 int ret;
67 int i;
68 void *p;
69
70 ret = posix_memalign(memptr: &p, alignment: 0x1000, size: vring_size(num: ring_size, align: 0x1000));
71 if (ret) {
72 perror(s: "Unable to allocate ring buffer.\n");
73 exit(status: 3);
74 }
75 memset(s: p, c: 0, n: vring_size(num: ring_size, align: 0x1000));
76 vring_init(vr: &ring, num: ring_size, p, align: 0x1000);
77
78 guest.avail_idx = 0;
79 guest.kicked_avail_idx = -1;
80 guest.last_used_idx = 0;
81#ifndef INORDER
82 /* Put everything in free lists. */
83 guest.free_head = 0;
84#endif
85 for (i = 0; i < ring_size - 1; i++)
86 ring.desc[i].next = i + 1;
87 host.used_idx = 0;
88 host.called_used_idx = -1;
89 guest.num_free = ring_size;
90 data = malloc(size: ring_size * sizeof *data);
91 if (!data) {
92 perror(s: "Unable to allocate data buffer.\n");
93 exit(status: 3);
94 }
95 memset(s: data, c: 0, n: ring_size * sizeof *data);
96}
97
98/* guest side */
99int add_inbuf(unsigned len, void *buf, void *datap)
100{
101 unsigned head;
102#ifndef INORDER
103 unsigned avail;
104#endif
105 struct vring_desc *desc;
106
107 if (!guest.num_free)
108 return -1;
109
110#ifdef INORDER
111 head = (ring_size - 1) & (guest.avail_idx++);
112#else
113 head = guest.free_head;
114#endif
115 guest.num_free--;
116
117 desc = ring.desc;
118 desc[head].flags = VRING_DESC_F_NEXT;
119 desc[head].addr = (unsigned long)(void *)buf;
120 desc[head].len = len;
121 /* We do it like this to simulate the way
122 * we'd have to flip it if we had multiple
123 * descriptors.
124 */
125 desc[head].flags &= ~VRING_DESC_F_NEXT;
126#ifndef INORDER
127 guest.free_head = desc[head].next;
128#endif
129
130 data[head].data = datap;
131
132#ifdef RING_POLL
133 /* Barrier A (for pairing) */
134 smp_release();
135 avail = guest.avail_idx++;
136 ring.avail->ring[avail & (ring_size - 1)] =
137 (head | (avail & ~(ring_size - 1))) ^ 0x8000;
138#else
139#ifndef INORDER
140 /* Barrier A (for pairing) */
141 smp_release();
142 avail = (ring_size - 1) & (guest.avail_idx++);
143 ring.avail->ring[avail] = head;
144#endif
145 /* Barrier A (for pairing) */
146 smp_release();
147#endif
148 ring.avail->idx = guest.avail_idx;
149 return 0;
150}
151
152void *get_buf(unsigned *lenp, void **bufp)
153{
154 unsigned head;
155 unsigned index;
156 void *datap;
157
158#ifdef RING_POLL
159 head = (ring_size - 1) & guest.last_used_idx;
160 index = ring.used->ring[head].id;
161 if ((index ^ guest.last_used_idx ^ 0x8000) & ~(ring_size - 1))
162 return NULL;
163 /* Barrier B (for pairing) */
164 smp_acquire();
165 index &= ring_size - 1;
166#else
167 if (ring.used->idx == guest.last_used_idx)
168 return NULL;
169 /* Barrier B (for pairing) */
170 smp_acquire();
171#ifdef INORDER
172 head = (ring_size - 1) & guest.last_used_idx;
173 index = head;
174#else
175 head = (ring_size - 1) & guest.last_used_idx;
176 index = ring.used->ring[head].id;
177#endif
178
179#endif
180#ifdef INORDER
181 *lenp = ring.desc[index].len;
182#else
183 *lenp = ring.used->ring[head].len;
184#endif
185 datap = data[index].data;
186 *bufp = (void*)(unsigned long)ring.desc[index].addr;
187 data[index].data = NULL;
188#ifndef INORDER
189 ring.desc[index].next = guest.free_head;
190 guest.free_head = index;
191#endif
192 guest.num_free++;
193 guest.last_used_idx++;
194 return datap;
195}
196
197bool used_empty()
198{
199 unsigned short last_used_idx = guest.last_used_idx;
200#ifdef RING_POLL
201 unsigned short head = last_used_idx & (ring_size - 1);
202 unsigned index = ring.used->ring[head].id;
203
204 return (index ^ last_used_idx ^ 0x8000) & ~(ring_size - 1);
205#else
206 return ring.used->idx == last_used_idx;
207#endif
208}
209
210void disable_call()
211{
212 /* Doing nothing to disable calls might cause
213 * extra interrupts, but reduces the number of cache misses.
214 */
215}
216
217bool enable_call()
218{
219 vring_used_event(&ring) = guest.last_used_idx;
220 /* Flush call index write */
221 /* Barrier D (for pairing) */
222 smp_mb();
223 return used_empty();
224}
225
226void kick_available(void)
227{
228 bool need;
229
230 /* Flush in previous flags write */
231 /* Barrier C (for pairing) */
232 smp_mb();
233 need = vring_need_event(vring_avail_event(&ring),
234 new_idx: guest.avail_idx,
235 old: guest.kicked_avail_idx);
236
237 guest.kicked_avail_idx = guest.avail_idx;
238 if (need)
239 kick();
240}
241
242/* host side */
243void disable_kick()
244{
245 /* Doing nothing to disable kicks might cause
246 * extra interrupts, but reduces the number of cache misses.
247 */
248}
249
250bool enable_kick()
251{
252 vring_avail_event(&ring) = host.used_idx;
253 /* Barrier C (for pairing) */
254 smp_mb();
255 return avail_empty();
256}
257
258bool avail_empty()
259{
260 unsigned head = host.used_idx;
261#ifdef RING_POLL
262 unsigned index = ring.avail->ring[head & (ring_size - 1)];
263
264 return ((index ^ head ^ 0x8000) & ~(ring_size - 1));
265#else
266 return head == ring.avail->idx;
267#endif
268}
269
270bool use_buf(unsigned *lenp, void **bufp)
271{
272 unsigned used_idx = host.used_idx;
273 struct vring_desc *desc;
274 unsigned head;
275
276#ifdef RING_POLL
277 head = ring.avail->ring[used_idx & (ring_size - 1)];
278 if ((used_idx ^ head ^ 0x8000) & ~(ring_size - 1))
279 return false;
280 /* Barrier A (for pairing) */
281 smp_acquire();
282
283 used_idx &= ring_size - 1;
284 desc = &ring.desc[head & (ring_size - 1)];
285#else
286 if (used_idx == ring.avail->idx)
287 return false;
288
289 /* Barrier A (for pairing) */
290 smp_acquire();
291
292 used_idx &= ring_size - 1;
293#ifdef INORDER
294 head = used_idx;
295#else
296 head = ring.avail->ring[used_idx];
297#endif
298 desc = &ring.desc[head];
299#endif
300
301 *lenp = desc->len;
302 *bufp = (void *)(unsigned long)desc->addr;
303
304#ifdef INORDER
305 desc->len = desc->len - 1;
306#else
307 /* now update used ring */
308 ring.used->ring[used_idx].id = head;
309 ring.used->ring[used_idx].len = desc->len - 1;
310#endif
311 /* Barrier B (for pairing) */
312 smp_release();
313 host.used_idx++;
314 ring.used->idx = host.used_idx;
315
316 return true;
317}
318
319void call_used(void)
320{
321 bool need;
322
323 /* Flush in previous flags write */
324 /* Barrier D (for pairing) */
325 smp_mb();
326 need = vring_need_event(vring_used_event(&ring),
327 new_idx: host.used_idx,
328 old: host.called_used_idx);
329
330 host.called_used_idx = host.used_idx;
331 if (need)
332 call();
333}
334

source code of linux/tools/virtio/ringtest/virtio_ring_0_9.c