[PATCH v3 3/4] powerpc/64s: idle POWER9 can execute stop in virtual mode

[Paul Mackerras]

On Fri, Aug 25, 2017 at 02:30:35PM +1000, Nicholas Piggin wrote:
> The hardware can execute stop in any context, and KVM does not
> require real mode because siblings do not share MMU state. This
> saves a switch to real-mode when going idle.
> 
> Acked-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin at 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 14e97f442167..32d65ee323a0 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -195,7 +195,16 @@ pnv_powersave_common:
>  	std	r5,_CCR(r1)
>  	std	r1,PACAR1(r13)
>  
> +BEGIN_FTR_SECTION
> +	/*
> +	 * POWER9 does not require real mode to stop, and presently 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

... and POWER7 too.

Since that's just a comment,

Reviewed-by: Paul Mackerras <paulus at ozlabs.org>