[PATCH] powernv:idle: Clear r12 on wakeup from stop lite

[PATCH] powernv:idle: Clear r12 on wakeup from stop lite

[Akshay Adiga]

pnv_wakeup_noloss expects R12 to contain SRR1 value to determine if
the wakeup reason is an HMI in CHECK_HMI_INTERRUPT.

When we wakeup with ESL=0, SRR1 will not contain the wakeup reason, so
there is no point setting R12 to SRR1.

However, we don't set R12 at all and R12 contains garbage, and still
being used to check HMI assuming that it had SRR1. causing the
OPAL msglog to be filled with the following print:
	HMI: Received HMI interrupt: HMER = 0x0040000000000000

This patch clears R12 after waking up from stop with ESL=EC=0, so that
we don't accidentally enter the HMI handler in pnv_wakeup_noloss if
the R12[42:45] corresponds to HMI as wakeup reason.

Bug existed prior to "commit 9d29250136f6 ("powerpc/64s/idle: Avoid SRR
usage in idle sleep/wake paths")  but was never hit in practice

Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Fixes: 9d29250136f6 ("powerpc/64s/idle: Avoid SRR usage in idle
sleep/wake paths")
---
 arch/powerpc/kernel/idle_book3s.S | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 1ea14b9..34794fd 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -256,6 +256,21 @@ power_enter_stop:
 	bne	 .Lhandle_esl_ec_set
 	IDLE_STATE_ENTER_SEQ(PPC_STOP)
 	li	r3,0  /* Since we didn't lose state, return 0 */
+	/*
+	 * pnv_wakeup_noloss expects R12 to contain SRR1 value
+	 * to determine if the wakeup reason is an HMI in
+	 * CHECK_HMI_INTERRUPT.
+	 *
+	 * However, when we wakeup with ESL=0,
+	 * SRR1 will not contain the wakeup reason,
+	 * so there is no point setting R12 to SRR1.
+	 *
+	 * Further, we clear R12 here, so that we
+	 * don't accidentally enter the HMI
+	 * in pnv_wakeup_noloss if the
+	 * R12[42:45] == WAKE_HMI.
+	 */
+	li	r12, 0
 	b 	pnv_wakeup_noloss
 
 .Lhandle_esl_ec_set:
-- 
2.5.5

Re: [PATCH] powernv:idle: Clear r12 on wakeup from stop lite

[Nicholas Piggin]

On Wed, 28 Jun 2017 06:46:49 +0530
Akshay Adiga <akshay.adiga@linux.vnet.ibm.com> wrote:

> pnv_wakeup_noloss expects R12 to contain SRR1 value to determine if
> the wakeup reason is an HMI in CHECK_HMI_INTERRUPT.
> 
> When we wakeup with ESL=0, SRR1 will not contain the wakeup reason, so
> there is no point setting R12 to SRR1.
> 
> However, we don't set R12 at all and R12 contains garbage, and still
> being used to check HMI assuming that it had SRR1. causing the
> OPAL msglog to be filled with the following print:
> 	HMI: Received HMI interrupt: HMER = 0x0040000000000000
> 
> This patch clears R12 after waking up from stop with ESL=EC=0, so that
> we don't accidentally enter the HMI handler in pnv_wakeup_noloss if
> the R12[42:45] corresponds to HMI as wakeup reason.
> 
> Bug existed prior to "commit 9d29250136f6 ("powerpc/64s/idle: Avoid SRR
> usage in idle sleep/wake paths")  but was never hit in practice
> 
> Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
> Fixes: 9d29250136f6 ("powerpc/64s/idle: Avoid SRR usage in idle
> sleep/wake paths")

Thanks guys, appreciate you finding and fixing my bug :)

I think this looks like the best fix. Really minor nitpick but you
could adjust the line widths on the comment slightly (mpe might do
that when merging).

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


> ---
>  arch/powerpc/kernel/idle_book3s.S | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 1ea14b9..34794fd 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -256,6 +256,21 @@ power_enter_stop:
>  	bne	 .Lhandle_esl_ec_set
>  	IDLE_STATE_ENTER_SEQ(PPC_STOP)
>  	li	r3,0  /* Since we didn't lose state, return 0 */
> +	/*
> +	 * pnv_wakeup_noloss expects R12 to contain SRR1 value
> +	 * to determine if the wakeup reason is an HMI in
> +	 * CHECK_HMI_INTERRUPT.
> +	 *
> +	 * However, when we wakeup with ESL=0,
> +	 * SRR1 will not contain the wakeup reason,
> +	 * so there is no point setting R12 to SRR1.
> +	 *
> +	 * Further, we clear R12 here, so that we
> +	 * don't accidentally enter the HMI
> +	 * in pnv_wakeup_noloss if the
> +	 * R12[42:45] == WAKE_HMI.
> +	 */
> +	li	r12, 0
>  	b 	pnv_wakeup_noloss
>  
>  .Lhandle_esl_ec_set:

Re: [PATCH] powernv:idle: Clear r12 on wakeup from stop lite

[Michael Ellerman]

Nicholas Piggin <npiggin@gmail.com> writes:

> On Wed, 28 Jun 2017 06:46:49 +0530
> Akshay Adiga <akshay.adiga@linux.vnet.ibm.com> wrote:
>
>> pnv_wakeup_noloss expects R12 to contain SRR1 value to determine if
>> the wakeup reason is an HMI in CHECK_HMI_INTERRUPT.
>> 
>> When we wakeup with ESL=0, SRR1 will not contain the wakeup reason, so
>> there is no point setting R12 to SRR1.
>> 
>> However, we don't set R12 at all and R12 contains garbage, and still
>> being used to check HMI assuming that it had SRR1. causing the
>> OPAL msglog to be filled with the following print:
>> 	HMI: Received HMI interrupt: HMER = 0x0040000000000000
>> 
>> This patch clears R12 after waking up from stop with ESL=EC=0, so that
>> we don't accidentally enter the HMI handler in pnv_wakeup_noloss if
>> the R12[42:45] corresponds to HMI as wakeup reason.
>> 
>> Bug existed prior to "commit 9d29250136f6 ("powerpc/64s/idle: Avoid SRR
>> usage in idle sleep/wake paths")  but was never hit in practice
>> 
>> Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
>> Fixes: 9d29250136f6 ("powerpc/64s/idle: Avoid SRR usage in idle
>> sleep/wake paths")
>
> Thanks guys, appreciate you finding and fixing my bug :)
>
> I think this looks like the best fix. Really minor nitpick but you
> could adjust the line widths on the comment slightly (mpe might do
> that when merging).

You know me too well :}

cheers

Re: powernv:idle: Clear r12 on wakeup from stop lite

[Michael Ellerman]

On Wed, 2017-06-28 at 01:16:49 UTC, Akshay Adiga wrote:
> pnv_wakeup_noloss expects R12 to contain SRR1 value to determine if
> the wakeup reason is an HMI in CHECK_HMI_INTERRUPT.
> 
> When we wakeup with ESL=0, SRR1 will not contain the wakeup reason, so
> there is no point setting R12 to SRR1.
> 
> However, we don't set R12 at all and R12 contains garbage, and still
> being used to check HMI assuming that it had SRR1. causing the
> OPAL msglog to be filled with the following print:
> 	HMI: Received HMI interrupt: HMER = 0x0040000000000000
> 
> This patch clears R12 after waking up from stop with ESL=EC=0, so that
> we don't accidentally enter the HMI handler in pnv_wakeup_noloss if
> the R12[42:45] corresponds to HMI as wakeup reason.
> 
> Bug existed prior to "commit 9d29250136f6 ("powerpc/64s/idle: Avoid SRR
> usage in idle sleep/wake paths")  but was never hit in practice
> 
> Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
> Fixes: 9d29250136f6 ("powerpc/64s/idle: Avoid SRR usage in idle
> sleep/wake paths")
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/4d0d7c02df680740da41f5f92a238c

cheers