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tcg/plugins: implement a qemu_plugin_user_exit helper

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In user-mode emulation there is a small race between preexit_cleanup
and exit_group() which means we may end up calling instrumented
instructions before the kernel reaps child threads. To solve this we
implement a new helper which ensures the callbacks are flushed along
with any translations before we let the host do it's a thing.

While we are at it make the documentation of
qemu_plugin_register_atexit_cb clearer as to what the user can expect.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Acked-by: Warner Losh <imp@bsdimp.com>
Message-Id: <20210720232703.10650-21-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée
2021-07-21 00:26:54 +01:00
parent 094d278547
commit f7e68c9c99
5 changed files with 68 additions and 4 deletions
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12
include/qemu/plugin.h
View File

@ -190,6 +190,16 @@ void qemu_plugin_add_dyn_cb_arr(GArray *arr);
void qemu_plugin_disable_mem_helpers(CPUState *cpu);
/**
* qemu_plugin_user_exit(): clean-up callbacks before calling exit callbacks
*
* This is a user-mode only helper that ensure we have fully cleared
* callbacks from all threads before calling the exit callbacks. This
* is so the plugins themselves don't have to jump through hoops to
* guard against race conditions.
*/
void qemu_plugin_user_exit(void);
#else /* !CONFIG_PLUGIN */
static inline void qemu_plugin_add_opts(void)
@ -250,6 +260,8 @@ void qemu_plugin_add_dyn_cb_arr(GArray *arr)
static inline void qemu_plugin_disable_mem_helpers(CPUState *cpu)
{ }
static inline void qemu_plugin_user_exit(void)
{ }
#endif /* !CONFIG_PLUGIN */
#endif /* QEMU_PLUGIN_H */

13
include/qemu/qemu-plugin.h
View File

@ -549,6 +549,19 @@ void qemu_plugin_vcpu_for_each(qemu_plugin_id_t id,
void qemu_plugin_register_flush_cb(qemu_plugin_id_t id,
qemu_plugin_simple_cb_t cb);
/**
* qemu_plugin_register_atexit_cb() - register exit callback
* @id: plugin ID
* @cb: callback
* @userdata: user data for callback
*
* The @cb function is called once execution has finished. Plugins
* should be able to free all their resources at this point much like
* after a reset/uninstall callback is called.
*
* In user-mode it is possible a few un-instrumented instructions from
* child threads may run before the host kernel reaps the threads.
*/
void qemu_plugin_register_atexit_cb(qemu_plugin_id_t id,
qemu_plugin_udata_cb_t cb, void *userdata);