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tcg: Prepare safe access to tb_flushed out of tb_lock 

Ensure atomicity and ordering of CPU's 'tb_flushed' access for future
translation block lookup out of 'tb_lock'.

This field can only be touched from another thread by tb_flush() in user
mode emulation. So the only access to be sequential atomic is:
 * a single write in tb_flush();
 * reads/writes out of 'tb_lock'.

In future, before enabling MTTCG in system mode, tb_flush() must be safe
and this field becomes unnecessary.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20160715175852.30749-5-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sergey Fedorov 2016-07-15 20:58:44 +03:00 committed by Paolo Bonzini
parent 89a16b1e42
commit 118b07308a
2 changed files with 9 additions and 11 deletions
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16
cpu-exec.c
View File

@ -338,13 +338,6 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
tb->flags != flags)) {
tb = tb_find_slow(cpu, pc, cs_base, flags);
}
if (cpu->tb_flushed) {
/* Ensure that no TB jump will be modified as the
* translation buffer has been flushed.
*/
last_tb = NULL;
cpu->tb_flushed = false;
}
#ifndef CONFIG_USER_ONLY
/* We don't take care of direct jumps when address mapping changes in
* system emulation. So it's not safe to make a direct jump to a TB
@ -356,7 +349,12 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
#endif
/* See if we can patch the calling TB. */
if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
tb_add_jump(last_tb, tb_exit, tb);
/* Check if translation buffer has been flushed */
if (cpu->tb_flushed) {
cpu->tb_flushed = false;
} else {
tb_add_jump(last_tb, tb_exit, tb);
}
}
tb_unlock();
return tb;
@ -617,7 +615,7 @@ int cpu_exec(CPUState *cpu)
break;
}
cpu->tb_flushed = false; /* reset before first TB lookup */
atomic_mb_set(&cpu->tb_flushed, false); /* reset before first TB lookup */
for(;;) {
cpu_handle_interrupt(cpu, &last_tb);
tb = tb_find_fast(cpu, last_tb, tb_exit);

4
translate-all.c
View File

@ -848,7 +848,6 @@ void tb_flush(CPUState *cpu)
> tcg_ctx.code_gen_buffer_size) {
cpu_abort(cpu, "Internal error: code buffer overflow\n");
}
tcg_ctx.tb_ctx.nb_tbs = 0;
CPU_FOREACH(cpu) {
int i;
@ -856,9 +855,10 @@ void tb_flush(CPUState *cpu)
for (i = 0; i < TB_JMP_CACHE_SIZE; ++i) {
atomic_set(&cpu->tb_jmp_cache[i], NULL);
}
cpu->tb_flushed = true;
atomic_mb_set(&cpu->tb_flushed, true);
}
tcg_ctx.tb_ctx.nb_tbs = 0;
qht_reset_size(&tcg_ctx.tb_ctx.htable, CODE_GEN_HTABLE_SIZE);
page_flush_tb();