[PATCH v7 18/33] x86/fred: add a NMI entry stub for FRED

[Xin Li]

From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>

On a FRED system, NMIs nest both with themselves and faults, transient
information is saved into the stack frame, and NMI unblocking only
happens when the stack frame indicates that so should happen.

Thus, the NMI entry stub for FRED is really quite small...

Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---
 arch/x86/include/asm/fred.h |  1 +
 arch/x86/kernel/nmi.c       | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index f670430aaa54..9ce2a6439091 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -99,6 +99,7 @@ static __always_inline unsigned long fred_event_data(struct pt_regs *regs)
 #define DEFINE_FRED_HANDLER(f) noinstr DECLARE_FRED_HANDLER(f)
 typedef DECLARE_FRED_HANDLER((*fred_handler));
 
+DECLARE_FRED_HANDLER(fred_exc_nmi);
 DECLARE_FRED_HANDLER(fred_exc_debug);
 DECLARE_FRED_HANDLER(fred_exc_page_fault);
 
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 776f4b1e395b..e7b2abe42583 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -34,6 +34,7 @@
 #include <asm/cache.h>
 #include <asm/nospec-branch.h>
 #include <asm/sev.h>
+#include <asm/fred.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/nmi.h>
@@ -643,6 +644,24 @@ void nmi_backtrace_stall_check(const struct cpumask *btp)
 
 #endif
 
+#ifdef CONFIG_X86_FRED
+DEFINE_FRED_HANDLER(fred_exc_nmi)
+{
+	/*
+	 * With FRED, CR2 and DR6 are pushed atomically on faults,
+	 * so we don't have to worry about saving and restoring them.
+	 * Breakpoint faults nest, so assume it is OK to leave DR7
+	 * enabled.
+	 */
+	irqentry_state_t irq_state = irqentry_nmi_enter(regs);
+
+	inc_irq_stat(__nmi_count);
+	default_do_nmi(regs);
+
+	irqentry_nmi_exit(regs, irq_state);
+}
+#endif
+
 void stop_nmi(void)
 {
 	ignore_nmis++;
-- 
2.34.1