diff mbox

[RESEND,v3,2/2] powernv: Fix MCE handler to avoid trashing CR0/CR1 registers.

Message ID 147064570604.6908.10782297574634779096.stgit@jupiter.in.ibm.com (mailing list archive)
State Superseded
Headers show

Commit Message

Mahesh J Salgaonkar Aug. 8, 2016, 8:41 a.m. UTC 
From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

The current implementation of MCE early handling modifies CR0/1 registers
without saving its old values. Fix this by moving early check for
powersaving mode to machine_check_handle_early().

The power architecture 2.06 or later allows the possibility of getting
machine check while in nap/sleep/winkle. The last bit of HSPRG0 is set
to 1, if thread is woken up from winkle. Hence, clear the last bit of
HSPRG0 (r13) before MCE handler starts using it as paca pointer.

Also, the current code always puts the thread into nap state irrespective
of whatever idle state it woke up from. Fix that by looking at
paca->thread_idle_state and put the thread back into same state where it
came from.

Cc: stable@vger.kernel.org
Reported-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Reviewed-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
---
Change in v3:
- Rebase to Linus' master.

Change in v2:
- Call IDLE_STATE_ENTER_SEQ(PPC_NAP) instead of power7_enter_nap_mode()
  to be consistent with other part of code.
---
 arch/powerpc/kernel/exceptions-64s.S |   69 ++++++++++++++++++++--------------
 1 file changed, 40 insertions(+), 29 deletions(-)

Comments

Michael Ellerman Aug. 8, 2016, 8:58 a.m. UTC | #1 
Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> writes:

> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>
> The current implementation of MCE early handling modifies CR0/1 registers
> without saving its old values. Fix this by moving early check for
> powersaving mode to machine_check_handle_early().
>
> The power architecture 2.06 or later allows the possibility of getting
> machine check while in nap/sleep/winkle. The last bit of HSPRG0 is set
> to 1, if thread is woken up from winkle. Hence, clear the last bit of
> HSPRG0 (r13) before MCE handler starts using it as paca pointer.
>
> Also, the current code always puts the thread into nap state irrespective
> of whatever idle state it woke up from. Fix that by looking at
> paca->thread_idle_state and put the thread back into same state where it
> came from.
>
> Cc: stable@vger.kernel.org

The information I need is "which commit introduced the bug".

Given that I can work out which stable releases we should backport the
patch to.

cheers
Mahesh J Salgaonkar Aug. 8, 2016, 9:17 a.m. UTC | #2 
On 08/08/2016 02:28 PM, Michael Ellerman wrote:
> Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> writes:
> 
>> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>>
>> The current implementation of MCE early handling modifies CR0/1 registers
>> without saving its old values. Fix this by moving early check for
>> powersaving mode to machine_check_handle_early().
>>
>> The power architecture 2.06 or later allows the possibility of getting
>> machine check while in nap/sleep/winkle. The last bit of HSPRG0 is set
>> to 1, if thread is woken up from winkle. Hence, clear the last bit of
>> HSPRG0 (r13) before MCE handler starts using it as paca pointer.
>>
>> Also, the current code always puts the thread into nap state irrespective
>> of whatever idle state it woke up from. Fix that by looking at
>> paca->thread_idle_state and put the thread back into same state where it
>> came from.
>>
>> Cc: stable@vger.kernel.org
> 
> The information I need is "which commit introduced the bug".

It fixes commit 1c51089: powerpc/book3s: Return from interrupt if coming
from evil context.

> Given that I can work out which stable releases we should backport the
> patch to.

It will need an backport to stable once it hits upstream.

-Mahesh.

> 
> cheers
>
diff mbox

Patch

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 694def6..a59c9cc 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -144,29 +144,14 @@  machine_check_pSeries_1:
 	 * vector
 	 */
 	SET_SCRATCH0(r13)		/* save r13 */
-#ifdef CONFIG_PPC_P7_NAP
-BEGIN_FTR_SECTION
-	/* Running native on arch 2.06 or later, check if we are
-	 * waking up from nap. We only handle no state loss and
-	 * supervisor state loss. We do -not- handle hypervisor
-	 * state loss at this time.
+	/*
+	 * Running native on arch 2.06 or later, we may wakeup from winkle
+	 * inside machine check. If yes, then last bit of HSPGR0 would be set
+	 * to 1. Hence clear it unconditionally.
 	 */
-	mfspr	r13,SPRN_SRR1
-	rlwinm.	r13,r13,47-31,30,31
-	OPT_GET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
-	beq	9f
-
-	mfspr	r13,SPRN_SRR1
-	rlwinm.	r13,r13,47-31,30,31
-	/* waking up from powersave (nap) state */
-	cmpwi	cr1,r13,2
-	/* Total loss of HV state is fatal. let's just stay stuck here */
-	OPT_GET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
-	bgt	cr1,.
-9:
-	OPT_SET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
-END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
-#endif /* CONFIG_PPC_P7_NAP */
+	GET_PACA(r13)
+	clrrdi	r13,r13,1
+	SET_PACA(r13)
 	EXCEPTION_PROLOG_0(PACA_EXMC)
 BEGIN_FTR_SECTION
 	b	machine_check_powernv_early
@@ -1273,25 +1258,51 @@  machine_check_handle_early:
 	 * Check if thread was in power saving mode. We come here when any
 	 * of the following is true:
 	 * a. thread wasn't in power saving mode
-	 * b. thread was in power saving mode with no state loss or
-	 *    supervisor state loss
+	 * b. thread was in power saving mode with no state loss,
+	 *    supervisor state loss or hypervisor state loss.
 	 *
-	 * Go back to nap again if (b) is true.
+	 * Go back to nap/sleep/winkle mode again if (b) is true.
 	 */
 	rlwinm.	r11,r12,47-31,30,31	/* Was it in power saving mode? */
 	beq	4f			/* No, it wasn;t */
 	/* Thread was in power saving mode. Go back to nap again. */
 	cmpwi	r11,2
-	bne	3f
-	/* Supervisor state loss */
+	blt	3f
+	/* Supervisor/Hypervisor state loss */
 	li	r0,1
 	stb	r0,PACA_NAPSTATELOST(r13)
 3:	bl	machine_check_queue_event
 	MACHINE_CHECK_HANDLER_WINDUP
 	GET_PACA(r13)
 	ld	r1,PACAR1(r13)
-	li	r3,PNV_THREAD_NAP
-	b	pnv_enter_arch207_idle_mode
+	/*
+	 * Check what idle state this CPU was in and go back to same mode
+	 * again.
+	 */
+	lbz	r3,PACA_THREAD_IDLE_STATE(r13)
+	cmpwi	r3,PNV_THREAD_NAP
+	bgt	10f
+	IDLE_STATE_ENTER_SEQ(PPC_NAP)
+	/* No return */
+10:
+	cmpwi	r3,PNV_THREAD_SLEEP
+	bgt	2f
+	IDLE_STATE_ENTER_SEQ(PPC_SLEEP)
+	/* No return */
+
+2:
+	/*
+	 * Go back to winkle. Please note that this thread was woken up in
+	 * machine check from winkle and have not restored the per-subcore
+	 * state. Hence before going back to winkle, set last bit of HSPGR0
+	 * to 1. This will make sure that if this thread gets woken up
+	 * again at reset vector 0x100 then it will get chance to restore
+	 * the subcore state.
+	 */
+	ori	r13,r13,1
+	SET_PACA(r13)
+	IDLE_STATE_ENTER_SEQ(PPC_WINKLE)
+	/* No return */
 4:
 #endif
 	/*