Re: [PATCH 12/13] powerpc/64s: idle POWER9 can execute stop in virtual mode

[Benjamin Herrenschmidt <benh@au1.ibm.com>]

On Sun, 2017-08-06 at 03:02 +1000, Nicholas Piggin wrote:
> The hardware can execute stop in any context, and KVM does not
> require real mode. This saves a switch to real-mode when going
> idle.

+Paulus.

> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/idle_book3s.S | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 75746111e2c4..8ac366a51bb5 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -141,7 +141,16 @@ pnv_powersave_common:
>  	std	r5,_CCR(r1)
>  	std	r1,PACAR1(r13)
>  
> +BEGIN_FTR_SECTION
> +	/*
> +	 * POWER9 does not require real mode to stop, and does not set
> +	 * hwthread_state for KVM (threads don't share MMU context), so
> +	 * we can remain in virtual mode for this.
> +	 */
> +	bctr
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
>  	/*
> +	 * POWER8
>  	 * Go to real mode to do the nap, as required by the architecture.
>  	 * Also, we need to be in real mode before setting hwthread_state,
>  	 * because as soon as we do that, another thread can switch