[Qemu-devel] [RFC] Starting a (secondary) CPU when it is halted or reset

[Ronald Hecht <ronald.hecht@gmx.de>]

Hello all,

I have a question regarding LEON SPARC SMP. In a LEON SPARC SMP system 
secondary CPUs (others that CPU#0) can be started by setting certain 
bits in the interrupt controller. At startup (reset) all CPUs are halted 
except CPU#0. In QEMU version 0.12 it was possible to simply set 
CPUSPARCState.halted to "0" to start a secondary CPU. This is no longer 
possible and reliable. The CPU that should be started does not wake up 
by doing this:

                 env->halted = 0;
                 qemu_cpu_kick(env);

It seems that the running CPU blocks the startup of the halted CPU. I 
need to notice, that the halted CPU has interrupts (and traps) disabled 
at startup. Thus, it is not possible to start the CPU by raising an 
interrupt.

I was playing with several things and I found that doing

                 env->halted = 0;
                 qemu_cpu_kick(env);
                 cpu_exit(cpu_single_env);

helps. The statement cpu_exit(cpu_single_env) forces the current CPU 
(cpu_single_env) to exit the execution loop and which allows to start 
the other CPU (env).

I'm unsure if this is the correct way to solve my problem. Any comments 
on this?

Thanks and best regards,
Ronald