Subject: [PATCH v2 11/14] powerpc/64s: machine check interrupt update NMI accounting

From: Nicholas Piggin <[email-masked]>
Date: Fri, 3 Apr 2020 23:26:19 +1000

machine_check_early is taken as an NMI, so nmi_enter is used there.
machine_check_exception is no longer taken as an NMI (it's invoked
via irq_work in the case a machine check hits in kernel mode), so
remove the nmi_enter from that case.

In NMI context, hash faults don't try to refill the hash table, which
can lead to crashes accessing non-pinned kernel pages. System reset
still has this potential problem.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/mce.c     |  7 +++++++
 arch/powerpc/kernel/process.c |  2 +-
 arch/powerpc/kernel/traps.c   | 13 +------------
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index 34c1001e9e8b..c1684be0d8b7 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -560,6 +560,9 @@ EXPORT_SYMBOL_GPL(machine_check_print_event_info);
 long machine_check_early(struct pt_regs *regs)
 {
 	long handled = 0;
+	bool nested = in_nmi();
+	if (!nested)
+		nmi_enter();
 
 	hv_nmi_check_nonrecoverable(regs);
 
@@ -568,6 +571,10 @@ long machine_check_early(struct pt_regs *regs)
 	 */
 	if (ppc_md.machine_check_early)
 		handled = ppc_md.machine_check_early(regs);
+
+	if (!nested)
+		nmi_exit();
+
 	return handled;
 }
 
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 1dea4d280f6f..f06d20678611 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1421,7 +1421,7 @@ void show_regs(struct pt_regs * regs)
 		pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
 #endif
 #ifdef CONFIG_PPC64
-	pr_cont("IRQMASK: %lx ", regs->softe);
+	pr_cont("IRQMASK: %lx IN_NMI:%d IN_MCE:%d", regs->softe, (int)get_paca()->in_nmi, (int)get_paca()->in_mce);
 #endif
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	if (MSR_TM_ACTIVE(regs->msr))
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 82a3438300fd..1845fd7e161a 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -823,9 +823,6 @@ int machine_check_generic(struct pt_regs *regs)
 void machine_check_exception(struct pt_regs *regs)
 {
 	int recover = 0;
-	bool nested = in_nmi();
-	if (!nested)
-		nmi_enter();
 
 	__this_cpu_inc(irq_stat.mce_exceptions);
 
@@ -851,20 +848,12 @@ void machine_check_exception(struct pt_regs *regs)
 	if (check_io_access(regs))
 		goto bail;
 
-	if (!nested)
-		nmi_exit();
-
 	die("Machine check", regs, SIGBUS);
 
+bail:
 	/* Must die if the interrupt is not recoverable */
 	if (!(regs->msr & MSR_RI))
 		nmi_panic(regs, "Unrecoverable Machine check");
-
-	return;
-
-bail:
-	if (!nested)
-		nmi_exit();
 }
 
 void SMIException(struct pt_regs *regs)
-- 
2.23.0