Re: [Qemu-ppc] [PATCH v2] spapr: ignore decr interrupts when MSR_EE is disabled

[Benjamin Herrenschmidt]

On Fri, 2017-07-14 at 09:34 +0530, Nikunj A Dadhania wrote:
> Rebooting a SMP TCG guest is broken for both single/multi threaded TCG.
> 
> When reset happens, all the CPUs are in halted state. First CPU is brought out
> of reset and secondary CPUs would be initialized by the guest kernel using a
> rtas call start-cpu.
> 
> However, in case of TCG, decrementer interrupts keep on coming and waking the
> secondary CPUs up.
> 
> These secondary CPUs would see the decrementer interrupt pending, which makes
> cpu::has_work() to bring them out of wait loop and start executing
> tcg_exec_cpu().
> 
> The problem with this is all the CPUs wake up and start booting SLOF image,
> causing the following exception(4 CPUs TCG VM):

This patch isn't right....

> --- a/target/ppc/translate_init.c
> +++ b/target/ppc/translate_init.c
> @@ -8536,7 +8536,8 @@ static bool cpu_has_work_POWER7(CPUState *cs)
>          }
>          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_DECR)) &&
>              (env->spr[SPR_LPCR] & LPCR_P7_PECE1)) {
> -            return true;
> +            /* Return true only when MSR_EE is enabled */
> +            return msr_ee;
>          }

No, the HW will not check MSR_EE, in fact, MSR_EE can purposefully be
left off and we might expect a wakeup still.

I think the right fix is for reset to clear the LPCR PECE bits.

 Cheers
Ben.
 
> >          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_MCK)) &&
>              (env->spr[SPR_LPCR] & LPCR_P7_PECE2)) {
> @@ -8693,7 +8694,8 @@ static bool cpu_has_work_POWER8(CPUState *cs)
>          }
>          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_DECR)) &&
>              (env->spr[SPR_LPCR] & LPCR_P8_PECE3)) {
> -            return true;
> +            /* Return true only when MSR_EE is enabled */
> +            return msr_ee;
>          }
>          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_MCK)) &&
>              (env->spr[SPR_LPCR] & LPCR_P8_PECE4)) {
> @@ -8876,7 +8878,8 @@ static bool cpu_has_work_POWER9(CPUState *cs)
>          /* Decrementer Exception */
>          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_DECR)) &&
>              (env->spr[SPR_LPCR] & LPCR_DEE)) {
> -            return true;
> +            /* Return true only when MSR_EE is enabled */
> +            return msr_ee;
>          }
>          /* Machine Check or Hypervisor Maintenance Exception */
>          if ((env->pending_interrupts & (1u << PPC_INTERRUPT_MCK |