Re: [PATCH v8 5/5] powernv/pseries: consolidate code for mce early handling.

On 08/23/2018 02:32 PM, Nicholas Piggin wrote:

On Thu, 23 Aug 2018 14:13:13 +0530
Mahesh Jagannath Salgaonkar [off-list ref] wrote:

quoted

On 08/20/2018 05:04 PM, Nicholas Piggin wrote:

quoted

On Sun, 19 Aug 2018 22:38:39 +0530
Mahesh J Salgaonkar [off-list ref] wrote:
  

quoted

From: Mahesh Salgaonkar <redacted>

Now that other platforms also implements real mode mce handler,
lets consolidate the code by sharing existing powernv machine check
early code. Rename machine_check_powernv_early to
machine_check_common_early and reuse the code.

Signed-off-by: Mahesh Salgaonkar <redacted>
---
 arch/powerpc/kernel/exceptions-64s.S |  155 ++++++----------------------------
 1 file changed, 28 insertions(+), 127 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 12f056179112..2f85a7baf026 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S

@@ -243,14 +243,13 @@ EXC_REAL_BEGIN(machine_check, 0x200, 0x100)
 	SET_SCRATCH0(r13)		/* save r13 */
 	EXCEPTION_PROLOG_0(PACA_EXMC)
 BEGIN_FTR_SECTION
-	b	machine_check_powernv_early
+	b	machine_check_common_early
 FTR_SECTION_ELSE
 	b	machine_check_pSeries_0
 ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
 EXC_REAL_END(machine_check, 0x200, 0x100)
 EXC_VIRT_NONE(0x4200, 0x100)
-TRAMP_REAL_BEGIN(machine_check_powernv_early)
-BEGIN_FTR_SECTION
+TRAMP_REAL_BEGIN(machine_check_common_early)
 	EXCEPTION_PROLOG_1(PACA_EXMC, NOTEST, 0x200)
 	/*
 	 * Register contents:

@@ -306,7 +305,9 @@ BEGIN_FTR_SECTION
 	/* Save r9 through r13 from EXMC save area to stack frame. */
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXMC)
 	mfmsr	r11			/* get MSR value */
+BEGIN_FTR_SECTION
 	ori	r11,r11,MSR_ME		/* turn on ME bit */
+END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	ori	r11,r11,MSR_RI		/* turn on RI bit */
 	LOAD_HANDLER(r12, machine_check_handle_early)
 1:	mtspr	SPRN_SRR0,r12

@@ -325,7 +326,6 @@ BEGIN_FTR_SECTION
 	andc	r11,r11,r10		/* Turn off MSR_ME */
 	b	1b
 	b	.	/* prevent speculative execution */
-END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 
 TRAMP_REAL_BEGIN(machine_check_pSeries)
 	.globl machine_check_fwnmi

@@ -333,7 +333,7 @@ machine_check_fwnmi:
 	SET_SCRATCH0(r13)		/* save r13 */
 	EXCEPTION_PROLOG_0(PACA_EXMC)
 BEGIN_FTR_SECTION
-	b	machine_check_pSeries_early
+	b	machine_check_common_early
 END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
 machine_check_pSeries_0:
 	EXCEPTION_PROLOG_1(PACA_EXMC, KVMTEST_PR, 0x200)

@@ -346,103 +346,6 @@ machine_check_pSeries_0:
 
 TRAMP_KVM_SKIP(PACA_EXMC, 0x200)
 
-TRAMP_REAL_BEGIN(machine_check_pSeries_early)
-BEGIN_FTR_SECTION
-	EXCEPTION_PROLOG_1(PACA_EXMC, NOTEST, 0x200)
-	mr	r10,r1			/* Save r1 */
-	lhz	r11,PACA_IN_MCE(r13)
-	cmpwi	r11,0			/* Are we in nested machine check */
-	bne	0f			/* Yes, we are. */
-	/* First machine check entry */
-	ld	r1,PACAMCEMERGSP(r13)	/* Use MC emergency stack */
-0:	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame */
-	addi	r11,r11,1		/* increment paca->in_mce */
-	sth	r11,PACA_IN_MCE(r13)
-	/* Limit nested MCE to level 4 to avoid stack overflow */
-	cmpwi	r11,MAX_MCE_DEPTH
-	bgt	1f			/* Check if we hit limit of 4 */
-	mfspr	r11,SPRN_SRR0		/* Save SRR0 */
-	mfspr	r12,SPRN_SRR1		/* Save SRR1 */
-	EXCEPTION_PROLOG_COMMON_1()
-	EXCEPTION_PROLOG_COMMON_2(PACA_EXMC)
-	EXCEPTION_PROLOG_COMMON_3(0x200)
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	BRANCH_LINK_TO_FAR(machine_check_early) /* Function call ABI */
-	ld	r12,_MSR(r1)
-	andi.	r11,r12,MSR_PR		/* See if coming from user. */
-	bne	2f			/* continue in V mode if we are. */
-
-	/*
-	 * At this point we are not sure about what context we come from.
-	 * We may be in the middle of swithing stack. r1 may not be valid.
-	 * Hence stay on emergency stack, call machine_check_exception and
-	 * return from the interrupt.
-	 * But before that, check if this is an un-recoverable exception.
-	 * If yes, then stay on emergency stack and panic.
-	 */
-	andi.	r11,r12,MSR_RI
-	beq	1f
-
-	/*
-	 * Check if we have successfully handled/recovered from error, if not
-	 * then stay on emergency stack and panic.
-	 */
-	cmpdi	r3,0		/* see if we handled MCE successfully */
-	beq	1f		/* if !handled then panic */
-
-	/* Stay on emergency stack and return from interrupt. */
-	LOAD_HANDLER(r10,mce_return)
-	mtspr	SPRN_SRR0,r10
-	ld	r10,PACAKMSR(r13)
-	mtspr	SPRN_SRR1,r10
-	RFI_TO_KERNEL
-	b	.
-
-1:	LOAD_HANDLER(r10,unrecover_mce)
-	mtspr	SPRN_SRR0,r10
-	ld	r10,PACAKMSR(r13)
-	/*
-	 * We are going down. But there are chances that we might get hit by
-	 * another MCE during panic path and we may run into unstable state
-	 * with no way out. Hence, turn ME bit off while going down, so that
-	 * when another MCE is hit during panic path, hypervisor will
-	 * power cycle the lpar, instead of getting into MCE loop.
-	 */
-	li	r3,MSR_ME
-	andc	r10,r10,r3		/* Turn off MSR_ME */
-	mtspr	SPRN_SRR1,r10
-	RFI_TO_KERNEL
-	b	.
-
-	/* Move original SRR0 and SRR1 into the respective regs */
-2:	ld	r9,_MSR(r1)
-	mtspr	SPRN_SRR1,r9
-	ld	r3,_NIP(r1)
-	mtspr	SPRN_SRR0,r3
-	ld	r9,_CTR(r1)
-	mtctr	r9
-	ld	r9,_XER(r1)
-	mtxer	r9
-	ld	r9,_LINK(r1)
-	mtlr	r9
-	REST_GPR(0, r1)
-	REST_8GPRS(2, r1)
-	REST_GPR(10, r1)
-	ld	r11,_CCR(r1)
-	mtcr	r11
-	/* Decrement paca->in_mce. */
-	lhz	r12,PACA_IN_MCE(r13)
-	subi	r12,r12,1
-	sth	r12,PACA_IN_MCE(r13)
-	REST_GPR(11, r1)
-	REST_2GPRS(12, r1)
-	/* restore original r1. */
-	ld	r1,GPR1(r1)
-	SET_SCRATCH0(r13)		/* save r13 */
-	EXCEPTION_PROLOG_0(PACA_EXMC)
-	b	machine_check_pSeries_0
-END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
-
 EXC_COMMON_BEGIN(machine_check_common)
 	/*
 	 * Machine check is different because we use a different

@@ -541,6 +444,9 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	bl	machine_check_early
 	std	r3,RESULT(r1)	/* Save result */
 	ld	r12,_MSR(r1)
+BEGIN_FTR_SECTION
+	b	4f
+END_FTR_SECTION_IFCLR(CPU_FTR_HVMODE)
 
 #ifdef	CONFIG_PPC_P7_NAP
 	/*

@@ -564,10 +470,11 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	 */
 	rldicl.	r11,r12,4,63		/* See if MC hit while in HV mode. */
 	beq	5f
-	andi.	r11,r12,MSR_PR		/* See if coming from user. */
+4:	andi.	r11,r12,MSR_PR		/* See if coming from user. */
 	bne	9f			/* continue in V mode if we are. */
 
 5:
+BEGIN_FTR_SECTION
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 	/*
 	 * We are coming from kernel context. Check if we are coming from

@@ -578,6 +485,7 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	cmpwi	r11,0			/* Check if coming from guest */
 	bne	9f			/* continue if we are. */
 #endif
+END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)  

Put these inside the ifdef?

  

quoted

 	/*
 	 * At this point we are not sure about what context we come from.
 	 * Queue up the MCE event and return from the interrupt.

@@ -611,6 +519,7 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	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

@@ -619,10 +528,24 @@ EXC_COMMON_BEGIN(machine_check_handle_early)
 	bl	machine_check_queue_event
 	MACHINE_CHECK_HANDLER_WINDUP
 	RFI_TO_USER_OR_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)  

Do you still need mce_return? Why can't you consolidate it as well? ...
Hmm, okay so now I look back at patch 2, I don't think you should call
machine_check_exception there. You're supposed to call
machine_check_queue_event here and it will be handled by irq work.  

machine_check_queue_event does not handle RTAS mce event.

Yes it would need a bit of work.

quoted

Also, we need
to call fwnmi_release_errinfo() as early as possible which is why I am
calling machine_check_exception() in mce_return path for pSeries.
Otherwise if we get another MCE before calling fwnmi_release_errinfo()
then lpar will get rebooted without any logs getting printed.

I think you can call that in your early handler, but then defer
the printing to the irq work.

Although hmm, maybe that's less of a problem now we do nmi_enter
in machine check exception so I think printk will use an NMI safe
buffer.

We have to be careful actually of soft irq state if we take a
machine check in an un-reconciled state or in the middle of
the irq replay code I'm not actually sure we do the right thing,
but that would be a bug in existing code too. And we definitely
have MSR[RI] vs DAR/DSISR bugs in existing code, sigh.

I don't know... maybe just push what you have and we'll try to do
some more fixes and cleanups on top of that.

Sure. I will respin the next version addressing your other minor
comments. Will work on more improvements as separate change.

Thanks,
-Mahesh.