Subject: [PATCH v2 10/16] powerpc/64s/exception: machine check pseries should skip the late handler for host kernel MCEs

From: Nicholas Piggin <[email-masked]>
Date: Thu, 11 Jul 2019 01:19:44 +1000

The powernv machine check handler copes with taking a MCE from one of
three contexts, guest, host kernel, and host user. In each case the
early handler runs first on a special stack. Then:

- The guest case branches to the KVM interrupt handler (via standard
  interrupt macros).
- The host user case will run the "late" handler which is like a
  normal interrupt that runs in virtual mode and uses the regular
  kernel stack.
- The host kernel case queues the event and schedules it for
  processing with irq work.

The last case is important, it must not enable virtual memory because
the MMU state may not be set up to deal with that (e.g., SLB might be
clear), it must not use the regular kernel stack for similar reasons
(e.g., might be in OPAL with OPAL stack in r1), and the kernel does
not expect anything to touch its stack if interrupts are disabled.

The pseries handler does not do this queueing, but instead it always
runs the late handler for host MCEs, which has some of the same
problems.

Now that pseries is using machine_check_events, it can just do the
same as powernv and queue up kernel-mode MCE events.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/exceptions-64s.S | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index f2c24a4ae723..ac7b5bb614d9 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1163,7 +1163,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
 	cmpdi	r3,0		/* see if we handled MCE successfully */
 
 	beq	1b		/* if !handled then panic */
-BEGIN_FTR_SECTION
+
 	/*
 	 * Return from MC interrupt.
 	 * Queue up the MCE event so that we can log it later, while
@@ -1172,18 +1172,7 @@ BEGIN_FTR_SECTION
 	bl	machine_check_queue_event
 	MACHINE_CHECK_HANDLER_WINDUP
 	RFI_TO_KERNEL
-FTR_SECTION_ELSE
-	/*
-	 * pSeries: Return from MC interrupt. Before that stay on emergency
-	 * stack and call machine_check_exception to log the MCE event.
-	 */
-	LOAD_HANDLER(r10,mce_return)
-	mtspr	SPRN_SRR0,r10
-	ld	r10,PACAKMSR(r13)
-	mtspr	SPRN_SRR1,r10
-	RFI_TO_KERNEL
-	b	.
-ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
+
 9:
 	/* Deliver the machine check to host kernel in V mode. */
 BEGIN_FTR_SECTION
@@ -1212,13 +1201,6 @@ EXC_COMMON_BEGIN(unrecover_mce)
 	bl	unrecoverable_exception
 	b	1b
 
-EXC_COMMON_BEGIN(mce_return)
-	/* Invoke machine_check_exception to print MCE event and return. */
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	machine_check_exception
-	MACHINE_CHECK_HANDLER_WINDUP
-	RFI_TO_KERNEL
-	b	.
 
 EXC_REAL_BEGIN(data_access, 0x300, 0x80)
 	EXCEPTION_PROLOG_0 PACA_EXGEN
-- 
2.20.1