[PATCH v4 01/11] x86/irq: Add enumeration of NMI source reporting CPU feature

[Jacob Pan]

The lack of a mechanism to pinpoint the origins of Non-Maskable Interrupts
(NMIs) necessitates that the NMI vector 2 handler consults each NMI source
handler individually. This approach leads to inefficiencies, delays, and
the occurrence of unnecessary NMIs, thereby also constraining the potential
applications of NMIs.

A new CPU feature, known as NMI source reporting, has been introduced as
part of the Flexible Return and Event Delivery (FRED) spec. This feature
enables the NMI vector 2 handler to directly obtain information about the
NMI source from the FRED event data.

The functionality of NMI source reporting is tied to the FRED. Although it
is enumerated by a unique CPUID feature bit, it cannot be turned off
independently once FRED is activated.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
v3: Removed CONFIG_X86_NMI_SOURCE (Li Xin, HPA, Sohil)
v2: Removed NMI source from static CPU ID dependency table (HPA)
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/traps.c            | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 3c7434329661..ec78d361e685 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -327,6 +327,7 @@
 #define X86_FEATURE_FRED		(12*32+17) /* Flexible Return and Event Delivery */
 #define X86_FEATURE_LKGS		(12*32+18) /* "" Load "kernel" (userspace) GS */
 #define X86_FEATURE_WRMSRNS		(12*32+19) /* "" Non-serializing WRMSR */
+#define X86_FEATURE_NMI_SOURCE		(12*32+20) /* NMI source reporting */
 #define X86_FEATURE_AMX_FP16		(12*32+21) /* "" AMX fp16 Support */
 #define X86_FEATURE_AVX_IFMA            (12*32+23) /* "" Support for VPMADD52[H,L]UQ */
 #define X86_FEATURE_LAM			(12*32+26) /* Linear Address Masking */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4fa0b17e5043..465f04e4a79f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1427,8 +1427,10 @@ early_param("fred", fred_setup);
 
 void __init trap_init(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
+	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred) {
 		setup_clear_cpu_cap(X86_FEATURE_FRED);
+		setup_clear_cpu_cap(X86_FEATURE_NMI_SOURCE);
+	}
 
 	/* Init cpu_entry_area before IST entries are set up */
 	setup_cpu_entry_areas();
-- 
2.25.1