[PATCH v6 24/24] arm64: Enable the support of pseudo-NMIs

[Julien Thierry <julien.thierry@arm.com>]

Add a build option and a command line parameter to build and enable the
support of pseudo-NMIs.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 arch/arm64/Kconfig                              | 14 ++++++++++++++
 arch/arm64/kernel/cpufeature.c                  | 11 ++++++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 81d1d5a..63dbd56 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1183,6 +1183,12 @@
 			to discrete, to make X server driver able to add WB
 			entry later. This parameter enables that.
 
+	enable_pseudo_nmi [ARM64]
+			Enables support for pseudo-NMIs in the kernel. This
+			requires both the kernel to be built with
+			CONFIG_ARM64_PSEUDO_NMI and to be running on a
+			platform with GICv3.
+
 	enable_timer_pin_1 [X86]
 			Enable PIN 1 of APIC timer
 			Can be useful to work around chipset bugs
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 787d785..4729cf0 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -958,6 +958,20 @@ config ARM64_SSBD
 
 	  If unsure, say Y.
 
+config ARM64_PSEUDO_NMI
+	bool "Support for NMI-like interrupts"
+	select CONFIG_ARM_GIC_V3
+	help
+	  Adds support for mimicking Non-Maskable Interrupts through the use of
+	  GIC interrupt priority. This support requires version 3 or later of
+	  Arm GIC.
+
+	  This high priority configuration for interrupts need to be
+	  explicitly enabled through the new kernel parameter
+	  "enable_pseudo_nmi".
+
+	  If unsure, say N
+
 menuconfig ARMV8_DEPRECATED
 	bool "Emulate deprecated/obsolete ARMv8 instructions"
 	depends on COMPAT
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 58a4978..acf1d06 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1149,10 +1149,19 @@ static void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused)
 #endif /* CONFIG_ARM64_RAS_EXTN */
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
+static bool enable_pseudo_nmi;
+
+static int __init early_enable_pseudo_nmi(char *p)
+{
+	enable_pseudo_nmi = true;
+	return 0;
+}
+early_param("enable_pseudo_nmi", early_enable_pseudo_nmi);
+
 static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 				   int scope)
 {
-	return false;
+	return enable_pseudo_nmi && has_useable_gicv3_cpuif(entry, scope);
 }
 #endif
 
-- 
1.9.1