Re: [PATCH v2 09/12] accel/tcg: Introduce EXCP_TB_FLUSH

[Paolo Bonzini <pbonzini@redhat.com>]

On 9/23/25 04:39, Richard Henderson wrote:
> We are going to disallow tb_flush from within the context
> of a running cpu.  Introduce a tcg-internal exception to
> return out of the cpu run loop and perform the flush there.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

One small difference is that different CPUs can fail tcg_tb_alloc() at 
the same time and flush multiple times.

I think the check on the generation count should remain.  Instead of 
introducing EXCP_TB_FLUSH, you can keep the guts of tb_flush() as

void tb_queue_flush(CPUState *cpu)
{
     unsigned tb_flush_count = qatomic_read(&tb_ctx.tb_flush_count);
     async_safe_run_on_cpu(cpu, do_tb_flush,
                           RUN_ON_CPU_HOST_INT(tb_flush_count));
}

With the unconditional async_safe_run_on_cpu() hidden behind a function, 
this patch goes away while the next one survives as

      if (unlikely(!tb)) {
-        /* flush must be done */
-        tb_flush(cpu);
          mmap_unlock();
-        /* Make the execution loop process the flush as soon as 
possible.  */
-        cpu->exception_index = EXCP_INTERRUPT;
+        tb_queue_flush(cpu);
          cpu_loop_exit(cpu);
      }

Paolo