[PATCH 1/6] 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>
---
 arch/x86/Kconfig                         | 9 +++++++++
 arch/x86/include/asm/cpufeatures.h       | 1 +
 arch/x86/include/asm/disabled-features.h | 8 +++++++-
 arch/x86/kernel/cpu/cpuid-deps.c         | 1 +
 arch/x86/kernel/traps.c                  | 4 +++-
 5 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1d7122a1883e..b8b15f20b94e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -511,12 +511,21 @@ config X86_CPU_RESCTRL
 config X86_FRED
 	bool "Flexible Return and Event Delivery"
 	depends on X86_64
+	select X86_NMI_SOURCE
 	help
 	  When enabled, try to use Flexible Return and Event Delivery
 	  instead of the legacy SYSCALL/SYSENTER/IDT architecture for
 	  ring transitions and exception/interrupt handling if the
 	  system supports it.
 
+config X86_NMI_SOURCE
+	def_bool n
+	help
+	  Once enabled, information on NMI originator/source can be provided
+	  via FRED event data. This makes NMI processing more efficient in that
+	  NMI handler does not need to check for every possible source at
+	  runtime when NMI is delivered.
+
 config X86_BIGSMP
 	bool "Support for big SMP systems with more than 8 CPUs"
 	depends on SMP && X86_32
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/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index c492bdc97b05..3856c4737d65 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -123,6 +123,12 @@
 # define DISABLE_FRED	(1 << (X86_FEATURE_FRED & 31))
 #endif
 
+#ifdef CONFIG_X86_NMI_SOURCE
+# define DISABLE_NMI_SOURCE	0
+#else
+# define DISABLE_NMI_SOURCE	(1 << (X86_FEATURE_NMI_SOURCE & 31))
+#endif
+
 #ifdef CONFIG_KVM_AMD_SEV
 #define DISABLE_SEV_SNP		0
 #else
@@ -145,7 +151,7 @@
 #define DISABLED_MASK10	0
 #define DISABLED_MASK11	(DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET| \
 			 DISABLE_CALL_DEPTH_TRACKING|DISABLE_USER_SHSTK)
-#define DISABLED_MASK12	(DISABLE_FRED|DISABLE_LAM)
+#define DISABLED_MASK12	(DISABLE_FRED|DISABLE_LAM|DISABLE_NMI_SOURCE)
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
 #define DISABLED_MASK15	0
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index b7d9f530ae16..3f1a1a1961fa 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -84,6 +84,7 @@ static const struct cpuid_dep cpuid_deps[] = {
 	{ X86_FEATURE_SHSTK,			X86_FEATURE_XSAVES    },
 	{ X86_FEATURE_FRED,			X86_FEATURE_LKGS      },
 	{ X86_FEATURE_FRED,			X86_FEATURE_WRMSRNS   },
+	{ X86_FEATURE_FRED,			X86_FEATURE_NMI_SOURCE},
 	{}
 };
 
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