[PATCH v3 5/9] x86/nmi: Support NMI stop-machine handler

["Chang S. Bae" <chang.seok.bae@intel.com>]

From: David Kaplan <david.kaplan@amd.com>

Call the stop-machine handler from the NMI path in order to support the
NMI stop-machine.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
---
Sashiko raises a concern about coalescing edge-triggered events, such as
PMU overflows. But, not sure whether a practical issue or not especially
with this stop-machine use.

The current use of this facility has been to the microcode loader. Then
the mentioned case sounds like somewhat careless setup. Thus, the concern
looks theoretical, leaving the handling as-is.
---
 arch/x86/kernel/nmi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 3c9f60d6ca5a..26f5ca1ac8a5 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -24,6 +24,7 @@
 #include <linux/export.h>
 #include <linux/atomic.h>
 #include <linux/sched/clock.h>
+#include <linux/stop_machine.h>
 #include <linux/kvm_types.h>
 
 #include <asm/cpu_entry_area.h>
@@ -382,6 +383,9 @@ static noinstr void default_do_nmi(struct pt_regs *regs)
 
 	instrumentation_begin();
 
+	if (stop_machine_nmi_handler())
+		goto out;
+
 	if (microcode_nmi_handler_enabled() && microcode_nmi_handler())
 		goto out;
 
-- 
2.53.0