[PATCH v2 13/14] powerpc/64s: idle POWER9 can execute stop in virtual mode

[Nicholas Piggin <npiggin@gmail.com>]

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@linux.vnet.ibm.com>
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 3b701b1a5e87..fc5145339277 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
-- 
2.13.3