Re: [PATCH v5 5/7] powerpc/pseries: flush SLB contents on SLB MCE errors.

On Tue, 3 Jul 2018 08:08:14 +1000
"Nicholas Piggin" [off-list ref] wrote:

On Mon, 02 Jul 2018 11:17:06 +0530
Mahesh J Salgaonkar [off-list ref] wrote:

quoted

From: Mahesh Salgaonkar <redacted>

On pseries, as of today system crashes if we get a machine check
exceptions due to SLB errors. These are soft errors and can be
fixed by flushing the SLBs so the kernel can continue to function
instead of system crash. We do this in real mode before turning on
MMU. Otherwise we would run into nested machine checks. This patch
now fetches the rtas error log in real mode and flushes the SLBs on
SLB errors.

Signed-off-by: Mahesh Salgaonkar <redacted>
---
 arch/powerpc/include/asm/book3s/64/mmu-hash.h |    1 
 arch/powerpc/include/asm/machdep.h            |    1 
 arch/powerpc/kernel/exceptions-64s.S          |   42
+++++++++++++++++++++ arch/powerpc/kernel/mce.c
|   16 +++++++- arch/powerpc/mm/slb.c                         |
6 +++ arch/powerpc/platforms/powernv/opal.c         |    1 
 arch/powerpc/platforms/pseries/pseries.h      |    1 
 arch/powerpc/platforms/pseries/ras.c          |   51
+++++++++++++++++++++++++
arch/powerpc/platforms/pseries/setup.c        |    1 9 files
changed, 116 insertions(+), 4 deletions(-) 

quoted

+TRAMP_REAL_BEGIN(machine_check_pSeries_early)
+BEGIN_FTR_SECTION
+	EXCEPTION_PROLOG_1(PACA_EXMC, NOTEST, 0x200)
+	mr	r10,r1			/* Save r1 */
+	ld	r1,PACAMCEMERGSP(r13)	/* Use MC emergency
stack */
+	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack
frame		*/
+	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 */  

Is there any reason you can't use the existing
machine_check_powernv_early code to do all this?

quoted

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index efdd16a79075..221271c96a57 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c

@@ -488,9 +488,21 @@ long machine_check_early(struct pt_regs *regs)
 {
 	long handled = 0;
 
-	__this_cpu_inc(irq_stat.mce_exceptions);
+	/*
+	 * For pSeries we count mce when we go into virtual mode

machine
+	 * check handler. Hence skip it. Also, We can't access per
cpu
+	 * variables in real mode for LPAR.
+	 */
+	if (early_cpu_has_feature(CPU_FTR_HVMODE))
+		__this_cpu_inc(irq_stat.mce_exceptions);
 
-	if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
+	/*
+	 * See if platform is capable of handling machine check.
+	 * Otherwise fallthrough and allow CPU to handle this
machine check.
+	 */
+	if (ppc_md.machine_check_early)
+		handled = ppc_md.machine_check_early(regs);
+	else if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
 		handled =
cur_cpu_spec->machine_check_early(regs);  

Would be good to add a powernv ppc_md handler which does the
cur_cpu_spec->machine_check_early() call now that other platforms are
calling this code. Because those aren't valid as a fallback call, but
specific to powernv.

Something like this (untested)?

Subject: [PATCH] powerpc/powernv: define platform MCE handler.

---
 arch/powerpc/kernel/mce.c              |  3 ---
 arch/powerpc/platforms/powernv/setup.c | 11 +++++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index 221271c96a57..ae17d8aa60c4 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c

@@ -498,12 +498,9 @@ long machine_check_early(struct pt_regs *regs)
 
 	/*
 	 * See if platform is capable of handling machine check.
-	 * Otherwise fallthrough and allow CPU to handle this machine check.
 	 */
 	if (ppc_md.machine_check_early)
 		handled = ppc_md.machine_check_early(regs);
-	else if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
-		handled = cur_cpu_spec->machine_check_early(regs);
 	return handled;
 }
 

diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index f96df0a25d05..b74c93bc2e55 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c

@@ -431,6 +431,16 @@ static unsigned long pnv_get_proc_freq(unsigned int cpu)
 	return ret_freq;
 }
 
+static long pnv_machine_check_early(struct pt_regs *regs)
+{
+	long handled = 0;
+
+	if (cur_cpu_spec && cur_cpu_spec->machine_check_early)
+		handled = cur_cpu_spec->machine_check_early(regs);
+
+	return handled;
+}
+
 define_machine(powernv) {
 	.name			= "PowerNV",
 	.probe			= pnv_probe,

@@ -442,6 +452,7 @@ define_machine(powernv) {
 	.machine_shutdown	= pnv_shutdown,
 	.power_save             = NULL,
 	.calibrate_decr		= generic_calibrate_decr,
+	.machine_check_early	= pnv_machine_check_early,
 #ifdef CONFIG_KEXEC_CORE
 	.kexec_cpu_down		= pnv_kexec_cpu_down,
 #endif

-- 
2.13.7