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Re: [Qemu-devel] [PATCH] mttcg: Set jmp_env to handle exit from tb_gen_c
From: |
Pranith Kumar |
Subject: |
Re: [Qemu-devel] [PATCH] mttcg: Set jmp_env to handle exit from tb_gen_code |
Date: |
Mon, 20 Feb 2017 18:56:23 -0500 |
User-agent: |
mu4e 0.9.18; emacs 25.1.1 |
Alex Bennée writes:
> Pranith Kumar <address@hidden> writes:
>
>> tb_gen_code() can exit execution using cpu_exit_loop() when it cannot
>> allocate new tb's. To handle this, we need to properly set the jmp_env
>> pointer ahead of calling tb_gen_code().
>>
>> CC:Alex Bennée <address@hidden>
>> CC: Richard Henderson <address@hidden>
>> Signed-off-by: Pranith Kumar <address@hidden>
>> ---
>> cpu-exec.c | 23 +++++++++++------------
>> 1 file changed, 11 insertions(+), 12 deletions(-)
>>
>> diff --git a/cpu-exec.c b/cpu-exec.c
>> index 97d79612d9..4b70988b24 100644
>> --- a/cpu-exec.c
>> +++ b/cpu-exec.c
>> @@ -236,23 +236,22 @@ static void cpu_exec_step(CPUState *cpu)
>>
>> cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
>> tb_lock();
>> - tb = tb_gen_code(cpu, pc, cs_base, flags,
>> - 1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
>> - tb->orig_tb = NULL;
>> - tb_unlock();
>> -
>> - cc->cpu_exec_enter(cpu);
>> -
>
> It occurs to me we are also diverging in our locking pattern from
> tb_find which takes mmap_lock first. This is a NOP for system emulation
> but needed for user-emulation (for which we can do cpu_exec_step but not
> cpu_exec_nocache).
Right. So we have to take the mmap_lock() before calling
tb_gen_code(). However, this lock is released in the error path before calling
cpu_loop_exit() if allocation of a new tb fails. The following is what I have
after merging with the previous EXCP_ATOMIC handling patch.
diff --git a/cpu-exec.c b/cpu-exec.c
index a8e04bffbf..2bb3ba3672 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -228,6 +228,7 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
static void cpu_exec_step(CPUState *cpu)
{
+ CPUClass *cc = CPU_GET_CLASS(cpu);
CPUArchState *env = (CPUArchState *)cpu->env_ptr;
TranslationBlock *tb;
target_ulong cs_base, pc;
@@ -235,16 +236,24 @@ static void cpu_exec_step(CPUState *cpu)
cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
tb_lock();
- tb = tb_gen_code(cpu, pc, cs_base, flags,
- 1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
- tb->orig_tb = NULL;
- tb_unlock();
- /* execute the generated code */
- trace_exec_tb_nocache(tb, pc);
- cpu_tb_exec(cpu, tb);
- tb_lock();
- tb_phys_invalidate(tb, -1);
- tb_free(tb);
+ if (sigsetjmp(cpu->jmp_env, 0) == 0) {
+ mmap_lock();
+ tb = tb_gen_code(cpu, pc, cs_base, flags,
+ 1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
+ tb->orig_tb = NULL;
+ mmap_unlock();
+ tb_unlock();
+
+ cc->cpu_exec_enter(cpu);
+ /* execute the generated code */
+ trace_exec_tb_nocache(tb, pc);
+ cpu_tb_exec(cpu, tb);
+ cc->cpu_exec_exit(cpu);
+
+ tb_lock();
+ tb_phys_invalidate(tb, -1);
+ tb_free(tb);
+ }
tb_unlock();
}
diff --git a/cpus.c b/cpus.c
index 77bba08f9a..b39408b4b1 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1347,6 +1347,11 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
if (r == EXCP_DEBUG) {
cpu_handle_guest_debug(cpu);
break;
+ } else if (r == EXCP_ATOMIC) {
+ qemu_mutex_unlock_iothread();
+ cpu_exec_step_atomic(cpu);
+ qemu_mutex_lock_iothread();
+ break;
}
} else if (cpu->stop) {
if (cpu->unplug) {
@@ -1457,6 +1462,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
*/
g_assert(cpu->halted);
break;
+ case EXCP_ATOMIC:
+ qemu_mutex_unlock_iothread();
+ cpu_exec_step_atomic(cpu);
+ qemu_mutex_lock_iothread();
default:
/* Ignore everything else? */
break;
--
Pranith