arm64: cpufeature: Detect HCR_EL2.NV1 being RES0

A variant of FEAT_E2H0 not being implemented exists in the form of
HCR_EL2.E2H being RES1 *and* HCR_EL2.NV1 being RES0 (indicating that
only VHE is supported on the host and nested guests).

Add the necessary infrastructure for this new CPU capability.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240122181344.258974-7-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kernel/cpufeature.c

@@ -1794,6 +1794,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 	return !meltdown_safe;
 }
 
+static bool has_nv1(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	return !has_cpuid_feature(entry, scope);
+}
+
 #if defined(ID_AA64MMFR0_EL1_TGRAN_LPA2) && defined(ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_LPA2)
 static bool has_lpa2_at_stage1(u64 mmfr0)
 {
@@ -2794,6 +2799,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
 		.matches = has_lpa2,
 	},
+	{
+		.desc = "NV1",
+		.capability = ARM64_HAS_HCR_NV1,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_nv1,
+		ARM64_CPUID_FIELDS_NEG(ID_AA64MMFR4_EL1, E2H0, NI_NV1)
+	},
 	{},
 };
 

arch/arm64/tools/cpucaps

@@ -35,6 +35,7 @@ HAS_GENERIC_AUTH_IMP_DEF
 HAS_GIC_CPUIF_SYSREGS
 HAS_GIC_PRIO_MASKING
 HAS_GIC_PRIO_RELAXED_SYNC
+HAS_HCR_NV1
 HAS_HCX
 HAS_LDAPR
 HAS_LPA2