Re: [Qemu-devel] [PATCH 2/2] spapr/rtas: do not reset the MSR in stop-self command

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Oct 05, 2017 at 06:49:59PM +0200, Cédric Le Goater wrote:
> When a CPU is stopped with the 'stop-self' RTAS call, its state
> 'halted' is switched to 1 and, in this case, the MSR is not taken into
> account anymore in the cpu_has_work() routine. Only the pending
> hardware interrupts are checked with their LPCR:PECE* enablement bit.
> 
> The CPU is now also protected from the decrementer interrupt by the
> LPCR:PECE* bits which are disabled in the 'stop-self' RTAS
> call. Reseting the MSR is pointless.
> 
> Signed-off-by: Cédric Le Goater <clg@kaod.org>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  hw/ppc/spapr_rtas.c | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 2389220c9738..7f5ddce89ef2 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -209,16 +209,6 @@ static void rtas_stop_self(PowerPCCPU *cpu, sPAPRMachineState *spapr,
>  
>      cs->halted = 1;
>      qemu_cpu_kick(cs);
> -    /*
> -     * While stopping a CPU, the guest calls H_CPPR which
> -     * effectively disables interrupts on XICS level.
> -     * However decrementer interrupts in TCG can still
> -     * wake the CPU up so here we disable interrupts in MSR
> -     * as well.
> -     * As rtas_start_cpu() resets the whole MSR anyway, there is
> -     * no need to bother with specific bits, we just clear it.
> -     */
> -    env->msr = 0;
>  
>      if (env->mmu_model == POWERPC_MMU_3_00) {
>          env->spr[SPR_LPCR] &= ~LPCR_DEE;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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