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

[Nicholas Piggin <npiggin@gmail.com>]

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
>  	 */
>