[PATCH v4 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>
---
V3 -> V4: Leave a note against coalesced NMI events in theory (Sashiko).
---
 arch/x86/kernel/nmi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 3c9f60d6ca5a..0d426e5e74ee 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 +383,14 @@ static noinstr void default_do_nmi(struct pt_regs *regs)
 
 	instrumentation_begin();
 
+	/*
+	 * When an NMI stop-machine runs, the rest of the system should be idle,
+	 * so handle the stop-machine NMI first even if other NMIs might get
+	 * coalesced with it.
+	 */
+	if (stop_machine_nmi_handler())
+		goto out;
+
 	if (microcode_nmi_handler_enabled() && microcode_nmi_handler())
 		goto out;
 
-- 
2.53.0