Re: [PATCH 4/8] powerpc/64s: fix POWER9 machine check handler from stop state

On Thu, 16 Mar 2017 18:10:48 +0530
Mahesh Jagannath Salgaonkar [off-list ref] wrote:

On 03/14/2017 02:53 PM, Nicholas Piggin wrote:

quoted

The ISA specifies power save wakeup can cause a machine check interrupt.
The machine check handler currently has code to handle that for POWER8,
but POWER9 crashes when trying to execute the P8 style sleep
instructions.

So queue up the machine check, then call into the idle code to wake up
as the system reset interrupt does, rather than attempting to sleep
again without going through the main idle path.

Reviewed-by: Gautham R. Shenoy <redacted>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/reg.h       |  1 +
 arch/powerpc/kernel/exceptions-64s.S | 69 ++++++++++++++++++------------------
 2 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index fc879fd6bdae..8bbdfacce970 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h

@@ -656,6 +656,7 @@
 #define   SRR1_ISI_PROT		0x08000000 /* ISI: Other protection fault */
 #define   SRR1_WAKEMASK		0x00380000 /* reason for wakeup */
 #define   SRR1_WAKEMASK_P8	0x003c0000 /* reason for wakeup on POWER8 and 9 */
+#define   SRR1_WAKEMCE_RESVD	0x003c0000 /* Unused/reserved value used by MCE wakeup to indicate cause to idle wakeup handler */
 #define   SRR1_WAKESYSERR	0x00300000 /* System error */
 #define   SRR1_WAKEEE		0x00200000 /* External interrupt */
 #define   SRR1_WAKEHVI		0x00240000 /* Hypervisor Virtualization Interrupt (P9) */

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index e390fcd04bcb..5779d2d6a192 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S

@@ -306,6 +306,33 @@ EXC_COMMON_BEGIN(machine_check_common)
 	/* restore original r1. */			\
 	ld	r1,GPR1(r1)

+#ifdef CONFIG_PPC_P7_NAP
+EXC_COMMON_BEGIN(machine_check_idle_common)
+	bl	machine_check_queue_event
+	/*
+	 * Queue the machine check, then reload SRR1 and use it to set
+	 * CR3 according to pnv_powersave_wakeup convention.
+	 */
+	ld	r12,_MSR(r1)
+	rlwinm	r11,r12,47-31,30,31
+	cmpwi	cr3,r11,2
+
+	/*
+	 * Now put SRR1_WAKEMCE_RESVD into SRR1, allows it to follow the
+	 * system reset wakeup code.
+	 */
+	oris	r12,r12,SRR1_WAKEMCE_RESVD@h
+	mtspr	SPRN_SRR1,r12
+	std	r12,_MSR(r1)
+
+	/*
+	 * Decrement MCE nesting after finishing with the stack.
+	 */
+	lhz	r11,PACA_IN_MCE(r13)
+	subi	r11,r11,1
+	sth	r11,PACA_IN_MCE(r13)  

Looks like we are not winding up.. Shouldn't we ? What if we may end up
in pnv_wakeup_noloss() which assumes that no GPRs are lost. Am I missing
anything ?

Hmm, on second look, I don't think any non-volatile GPRs are overwritten
in this path. But this MCE is a slow path, and it is a much longer path
than the system reset idle wakeup... So I'll add the napstatelost with
a comment.

Thanks,
Nick