[v2] powerpc: Invalidate ERAT on powersave wakeup for POWER9

On POWER9 the ERAT may be incorrect on wakeup from some stop states
that lose state. This causes random segvs and illegal instructions
when these stop states are enabled.

This patch invalidates the ERAT on wakeup on POWER9 to prevent this
from causing a problem.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

v2. [BenH] Move to a place before we branch off to KVM if the
           core was in a guest. Also add a comment about the
           SRR1 bit extraction.
---
 arch/powerpc/kernel/exceptions-64s.S | 4 +++-
 arch/powerpc/kernel/idle_book3s.S    | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

On Sat, 24 Jun 2017 12:29:01 -0500
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On POWER9 the ERAT may be incorrect on wakeup from some stop states
> that lose state. This causes random segvs and illegal instructions
> when these stop states are enabled.
> 
> This patch invalidates the ERAT on wakeup on POWER9 to prevent this
> from causing a problem.
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
> 
> v2. [BenH] Move to a place before we branch off to KVM if the
>            core was in a guest. Also add a comment about the
>            SRR1 bit extraction.

This looks a bit safer to me now (avoiding KVM). My understanding is
the real-mode i- and d-ERAT entries are still valid and usable,
which is why this works.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> ---
>  arch/powerpc/kernel/exceptions-64s.S | 4 +++-
>  arch/powerpc/kernel/idle_book3s.S    | 7 +++++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index ae418b85c17c..b4b2c3a344c4 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -99,7 +99,9 @@ EXC_VIRT_NONE(0x4000, 0x100)
>  #ifdef CONFIG_PPC_P7_NAP
>  	/*
>  	 * If running native on arch 2.06 or later, check if we are waking up
> -	 * from nap/sleep/winkle, and branch to idle handler.
> +	 * from nap/sleep/winkle, and branch to idle handler. This tests
> +	 * SRR1 bits 46:47. A non-0 value indicates that we are coming from
> +	 * a power saving state.
>  	 */
>  #define IDLETEST(n)							\
>  	BEGIN_FTR_SECTION ;						\
> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 4898d676dcae..3fd65739e105 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -489,6 +489,13 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
>   */
>  pnv_restore_hyp_resource_arch300:
>  	/*
> +	 * Workaround for POWER9, if we lost resources, the ERAT
> +	 * might have been mixed up and needs flushing.
> +	 */
> +	blt	cr3,1f
> +	PPC_INVALIDATE_ERAT
> +1:
> +	/*
>  	 * POWER ISA 3. Use PSSCR to determine if we
>  	 * are waking up from deep idle state
>  	 */
>

On Sat, 2017-06-24 at 17:29:01 UTC, Benjamin Herrenschmidt wrote:
> On POWER9 the ERAT may be incorrect on wakeup from some stop states
> that lose state. This causes random segvs and illegal instructions
> when these stop states are enabled.
> 
> This patch invalidates the ERAT on wakeup on POWER9 to prevent this
> from causing a problem.
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/ba6d334ac230065243a92bb7cb3fd6

cheers