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Subject: [PATCH 2/9] arm64/cpufeature: Detect PE support for FEAT_NMI
Date: Tue, 9 Apr 2024 01:23:37 +0000
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From: Mark Brown <broonie@kernel.org>

Use of FEAT_NMI requires that all the PEs in the system and the GIC have
NMI support. This patch implements the PE part of that detection.

In order to avoid problematic interactions between real and pseudo NMIs
we disable the architected feature if the user has enabled pseudo NMIs
on the command line. If this is done on a system where support for the
architected feature is detected then a warning is printed during boot in
order to help users spot what is likely to be a misconfiguration.

In order to allow KVM to offer the feature to guests even if pseudo NMIs
are in use by the host we have a separate feature for the raw feature
which is used in KVM.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h |  6 +++
 arch/arm64/kernel/cpufeature.c      | 66 ++++++++++++++++++++++++++++-
 arch/arm64/tools/cpucaps            |  2 +
 3 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 8b904a757bd3..dc8b2d0d3763 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -800,6 +800,12 @@ static __always_inline bool system_uses_irq_prio_masking(void)
 	return alternative_has_cap_unlikely(ARM64_HAS_GIC_PRIO_MASKING);
 }
 
+static __always_inline bool system_uses_nmi(void)
+{
+	return IS_ENABLED(CONFIG_ARM64_NMI) &&
+		cpus_have_const_cap(ARM64_USES_NMI);
+}
+
 static inline bool system_supports_mte(void)
 {
 	return alternative_has_cap_unlikely(ARM64_MTE);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 56583677c1f2..fb9e52c84fda 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -85,6 +85,7 @@
 #include <asm/kvm_host.h>
 #include <asm/mmu_context.h>
 #include <asm/mte.h>
+#include <asm/nmi.h>
 #include <asm/processor.h>
 #include <asm/smp.h>
 #include <asm/sysreg.h>
@@ -291,6 +292,7 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr1[] = {
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_NMI_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SME),
 		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_SME_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_MPAM_frac_SHIFT, 4, 0),
@@ -1076,9 +1078,11 @@ static void init_32bit_cpu_features(struct cpuinfo_32bit *info)
 	init_cpu_ftr_reg(SYS_MVFR2_EL1, info->reg_mvfr2);
 }
 
-#ifdef CONFIG_ARM64_PSEUDO_NMI
+#if IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) || IS_ENABLED(CONFIG_ARM64_NMI)
 static bool enable_pseudo_nmi;
+#endif
 
+#ifdef CONFIG_ARM64_PSEUDO_NMI
 static int __init early_enable_pseudo_nmi(char *p)
 {
 	return kstrtobool(p, &enable_pseudo_nmi);
@@ -2263,6 +2267,41 @@ static bool has_gic_prio_relaxed_sync(const struct arm64_cpu_capabilities *entry
 }
 #endif
 
+#ifdef CONFIG_ARM64_NMI
+static bool use_nmi(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	if (!has_cpuid_feature(entry, scope))
+		return false;
+
+	/*
+	 * Having both real and pseudo NMIs enabled simultaneously is
+	 * likely to cause confusion.  Since pseudo NMIs must be
+	 * enabled with an explicit command line option, if the user
+	 * has set that option on a system with real NMIs for some
+	 * reason assume they know what they're doing.
+	 */
+	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && enable_pseudo_nmi) {
+		pr_info("Pseudo NMI enabled, not using architected NMI\n");
+		return false;
+	}
+
+	return true;
+}
+
+static void nmi_enable(const struct arm64_cpu_capabilities *__unused)
+{
+	/*
+	 * Enable use of NMIs controlled by ALLINT, SPINTMASK should
+	 * be clear by default but make it explicit that we are using
+	 * this mode.  Ensure that ALLINT is clear first in order to
+	 * avoid leaving things masked.
+	 */
+	_allint_clear();
+	sysreg_clear_set(sctlr_el1, SCTLR_EL1_SPINTMASK, SCTLR_EL1_NMI);
+	isb();
+}
+#endif
+
 #ifdef CONFIG_ARM64_BTI
 static void bti_enable(const struct arm64_cpu_capabilities *__unused)
 {
@@ -2861,6 +2900,31 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = has_nv1,
 		ARM64_CPUID_FIELDS_NEG(ID_AA64MMFR4_EL1, E2H0, NI_NV1)
 	},
+#ifdef CONFIG_ARM64_NMI
+	{
+		.desc = "Non-maskable Interrupts present",
+		.capability = ARM64_HAS_NMI,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.sys_reg = SYS_ID_AA64PFR1_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64PFR1_EL1_NMI_SHIFT,
+		.field_width = 4,
+		.min_field_value = ID_AA64PFR1_EL1_NMI_IMP,
+		.matches = has_cpuid_feature,
+	},
+	{
+		.desc = "Non-maskable Interrupts enabled",
+		.capability = ARM64_USES_NMI,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.sys_reg = SYS_ID_AA64PFR1_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64PFR1_EL1_NMI_SHIFT,
+		.field_width = 4,
+		.min_field_value = ID_AA64PFR1_EL1_NMI_IMP,
+		.matches = use_nmi,
+		.cpu_enable = nmi_enable,
+	},
+#endif
 	{},
 };
 
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 62b2838a231a..bb62c487ef99 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -43,6 +43,7 @@ HAS_LPA2
 HAS_LSE_ATOMICS
 HAS_MOPS
 HAS_NESTED_VIRT
+HAS_NMI
 HAS_PAN
 HAS_S1PIE
 HAS_RAS_EXTN
@@ -71,6 +72,7 @@ SPECTRE_BHB
 SSBS
 SVE
 UNMAP_KERNEL_AT_EL0
+USES_NMI
 WORKAROUND_834220
 WORKAROUND_843419
 WORKAROUND_845719
-- 
2.34.1