jcs.org
qemu with hax to log dma reads & writes
jcs.org/2018/11/12/vfio
1/*
2 * ucontext coroutine initialization code
3 *
4 * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
5 * Copyright (C) 2011 Kevin Wolf <kwolf@redhat.com>
6 *
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.0 of the License, or (at your option) any later version.
11 *
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
19 */
20
21/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
22#ifdef _FORTIFY_SOURCE
23#undef _FORTIFY_SOURCE
24#endif
25#include "qemu/osdep.h"
26#include <ucontext.h>
27#include "qemu/coroutine_int.h"
28
29#ifdef CONFIG_VALGRIND_H
30#include <valgrind/valgrind.h>
31#endif
32
33#if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
34#ifdef CONFIG_ASAN_IFACE_FIBER
35#define CONFIG_ASAN 1
36#include <sanitizer/asan_interface.h>
37#endif
38#endif
39
40#ifdef CONFIG_TSAN
41#include <sanitizer/tsan_interface.h>
42#endif
43
44typedef struct {
45 Coroutine base;
46 void *stack;
47 size_t stack_size;
48#ifdef CONFIG_SAFESTACK
49 /* Need an unsafe stack for each coroutine */
50 void *unsafe_stack;
51 size_t unsafe_stack_size;
52#endif
53 sigjmp_buf env;
54
55 void *tsan_co_fiber;
56 void *tsan_caller_fiber;
57
58#ifdef CONFIG_VALGRIND_H
59 unsigned int valgrind_stack_id;
60#endif
61
62} CoroutineUContext;
63
64/**
65 * Per-thread coroutine bookkeeping
66 */
67static __thread CoroutineUContext leader;
68static __thread Coroutine *current;
69
70/*
71 * va_args to makecontext() must be type 'int', so passing
72 * the pointer we need may require several int args. This
73 * union is a quick hack to let us do that
74 */
75union cc_arg {
76 void *p;
77 int i[2];
78};
79
80/* QEMU_ALWAYS_INLINE only does so if __OPTIMIZE__, so we cannot use it. */
81static inline __attribute__((always_inline))
82void on_new_fiber(CoroutineUContext *co)
83{
84#ifdef CONFIG_TSAN
85 co->tsan_co_fiber = __tsan_create_fiber(0); /* flags: sync on switch */
86 co->tsan_caller_fiber = __tsan_get_current_fiber();
87#endif
88}
89
90static inline __attribute__((always_inline))
91void finish_switch_fiber(void *fake_stack_save)
92{
93#ifdef CONFIG_ASAN
94 const void *bottom_old;
95 size_t size_old;
96
97 __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
98
99 if (!leader.stack) {
100 leader.stack = (void *)bottom_old;
101 leader.stack_size = size_old;
102 }
103#endif
104#ifdef CONFIG_TSAN
105 if (fake_stack_save) {
106 __tsan_release(fake_stack_save);
107 __tsan_switch_to_fiber(fake_stack_save, 0); /* 0=synchronize */
108 }
109#endif
110}
111
112static inline __attribute__((always_inline)) void start_switch_fiber(
113 CoroutineAction action, void **fake_stack_save,
114 const void *bottom, size_t size, void *new_fiber)
115{
116#ifdef CONFIG_ASAN
117 __sanitizer_start_switch_fiber(
118 action == COROUTINE_TERMINATE ? NULL : fake_stack_save,
119 bottom, size);
120#endif
121#ifdef CONFIG_TSAN
122 void *curr_fiber =
123 __tsan_get_current_fiber();
124 __tsan_acquire(curr_fiber);
125
126 *fake_stack_save = curr_fiber;
127 __tsan_switch_to_fiber(new_fiber, 0); /* 0=synchronize */
128#endif
129}
130
131static void coroutine_trampoline(int i0, int i1)
132{
133 union cc_arg arg;
134 CoroutineUContext *self;
135 Coroutine *co;
136 void *fake_stack_save = NULL;
137
138 finish_switch_fiber(NULL);
139
140 arg.i[0] = i0;
141 arg.i[1] = i1;
142 self = arg.p;
143 co = &self->base;
144
145 /* Initialize longjmp environment and switch back the caller */
146 if (!sigsetjmp(self->env, 0)) {
147 start_switch_fiber(
148 COROUTINE_YIELD,
149 &fake_stack_save,
150 leader.stack,
151 leader.stack_size,
152 self->tsan_caller_fiber);
153 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
154 }
155
156 finish_switch_fiber(fake_stack_save);
157
158 while (true) {
159 co->entry(co->entry_arg);
160 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
161 }
162}
163
164Coroutine *qemu_coroutine_new(void)
165{
166 CoroutineUContext *co;
167 ucontext_t old_uc, uc;
168 sigjmp_buf old_env;
169 union cc_arg arg = {0};
170 void *fake_stack_save = NULL;
171
172 /* The ucontext functions preserve signal masks which incurs a
173 * system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not
174 * preserve signal masks but only works on the current stack.
175 * Since we need a way to create and switch to a new stack, use
176 * the ucontext functions for that but sigsetjmp()/siglongjmp() for
177 * everything else.
178 */
179
180 if (getcontext(&uc) == -1) {
181 abort();
182 }
183
184 co = g_malloc0(sizeof(*co));
185 co->stack_size = COROUTINE_STACK_SIZE;
186 co->stack = qemu_alloc_stack(&co->stack_size);
187#ifdef CONFIG_SAFESTACK
188 co->unsafe_stack_size = COROUTINE_STACK_SIZE;
189 co->unsafe_stack = qemu_alloc_stack(&co->unsafe_stack_size);
190#endif
191 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
192
193 uc.uc_link = &old_uc;
194 uc.uc_stack.ss_sp = co->stack;
195 uc.uc_stack.ss_size = co->stack_size;
196 uc.uc_stack.ss_flags = 0;
197
198#ifdef CONFIG_VALGRIND_H
199 co->valgrind_stack_id =
200 VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
201#endif
202
203 arg.p = co;
204
205 on_new_fiber(co);
206 makecontext(&uc, (void (*)(void))coroutine_trampoline,
207 2, arg.i[0], arg.i[1]);
208
209 /* swapcontext() in, siglongjmp() back out */
210 if (!sigsetjmp(old_env, 0)) {
211 start_switch_fiber(
212 COROUTINE_YIELD,
213 &fake_stack_save,
214 co->stack, co->stack_size, co->tsan_co_fiber);
215
216#ifdef CONFIG_SAFESTACK
217 /*
218 * Before we swap the context, set the new unsafe stack
219 * The unsafe stack grows just like the normal stack, so start from
220 * the last usable location of the memory area.
221 * NOTE: we don't have to re-set the usp afterwards because we are
222 * coming back to this context through a siglongjmp.
223 * The compiler already wrapped the corresponding sigsetjmp call with
224 * code that saves the usp on the (safe) stack before the call, and
225 * restores it right after (which is where we return with siglongjmp).
226 */
227 void *usp = co->unsafe_stack + co->unsafe_stack_size;
228 __safestack_unsafe_stack_ptr = usp;
229#endif
230
231 swapcontext(&old_uc, &uc);
232 }
233
234 finish_switch_fiber(fake_stack_save);
235
236 return &co->base;
237}
238
239#ifdef CONFIG_VALGRIND_H
240#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
241/* Work around an unused variable in the valgrind.h macro... */
242#pragma GCC diagnostic push
243#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
244#endif
245static inline void valgrind_stack_deregister(CoroutineUContext *co)
246{
247 VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
248}
249#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
250#pragma GCC diagnostic pop
251#endif
252#endif
253
254void qemu_coroutine_delete(Coroutine *co_)
255{
256 CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
257
258#ifdef CONFIG_VALGRIND_H
259 valgrind_stack_deregister(co);
260#endif
261
262 qemu_free_stack(co->stack, co->stack_size);
263#ifdef CONFIG_SAFESTACK
264 qemu_free_stack(co->unsafe_stack, co->unsafe_stack_size);
265#endif
266 g_free(co);
267}
268
269/* This function is marked noinline to prevent GCC from inlining it
270 * into coroutine_trampoline(). If we allow it to do that then it
271 * hoists the code to get the address of the TLS variable "current"
272 * out of the while() loop. This is an invalid transformation because
273 * the sigsetjmp() call may be called when running thread A but
274 * return in thread B, and so we might be in a different thread
275 * context each time round the loop.
276 */
277CoroutineAction __attribute__((noinline))
278qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
279 CoroutineAction action)
280{
281 CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
282 CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
283 int ret;
284 void *fake_stack_save = NULL;
285
286 current = to_;
287
288 ret = sigsetjmp(from->env, 0);
289 if (ret == 0) {
290 start_switch_fiber(action, &fake_stack_save,
291 to->stack, to->stack_size, to->tsan_co_fiber);
292 siglongjmp(to->env, action);
293 }
294
295 finish_switch_fiber(fake_stack_save);
296
297 return ret;
298}
299
300Coroutine *qemu_coroutine_self(void)
301{
302 if (!current) {
303 current = &leader.base;
304 }
305#ifdef CONFIG_TSAN
306 if (!leader.tsan_co_fiber) {
307 leader.tsan_co_fiber = __tsan_get_current_fiber();
308 }
309#endif
310 return current;
311}
312
313bool qemu_in_coroutine(void)
314{
315 return current && current->caller;
316}