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powerpc/64s: idle POWER9 can execute stop in virtual mode 

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>
Reviewed-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2017-08-25 14:30:35 +10:00 committed by Michael Ellerman
parent 65dbbe812f
commit 72b0d51d97
1 changed files with 9 additions and 0 deletions
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arch/powerpc/kernel/idle_book3s.S
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@ -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
* 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