FEAT_BBM level 2 is useful to split large page table without breaking
the page table entry.  The following patch will use to improve
performance.  Detect it in cpufeature and use BOOT_CPU feature for now,
if the late CPU cores have conflict, kernel will not bring them up.

Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
---
 arch/arm64/include/asm/cpufeature.h | 15 +++++++++++++++
 arch/arm64/kernel/cpufeature.c      | 11 +++++++++++
 arch/arm64/tools/cpucaps            |  1 +
 3 files changed, 27 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 3d261cc123c1..c7ca5f9f88bb 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -838,6 +838,21 @@ static inline bool system_supports_poe(void)
 		alternative_has_cap_unlikely(ARM64_HAS_S1POE);
 }
 
+static inline bool system_supports_bbmlv2(void)
+{
+	return cpus_have_final_boot_cap(ARM64_HAS_BBMLV2);
+}
+
+static inline bool bbmlv2_available(void)
+{
+	u64 mmfr2;
+	u32 bbm;
+
+	mmfr2 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR2_EL1);
+	bbm = cpuid_feature_extract_unsigned_field(mmfr2, ID_AA64MMFR2_EL1_BBM_SHIFT);
+	return bbm == ID_AA64MMFR2_EL1_BBM_2;
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 718728a85430..cb916747cd31 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1866,6 +1866,11 @@ static bool has_lpa2(const struct arm64_cpu_capabilities *entry, int scope)
 }
 #endif
 
+static bool has_bbmlv2(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	return bbmlv2_available();
+}
+
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 #define KPTI_NG_TEMP_VA		(-(1UL << PMD_SHIFT))
 
@@ -2890,6 +2895,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		ARM64_CPUID_FIELDS(ID_AA64MMFR3_EL1, S1POE, IMP)
 	},
 #endif
+	{
+		.desc = "BBM Level 2",
+		.capability = ARM64_HAS_BBMLV2,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.matches = has_bbmlv2,
+	},
 	{},
 };
 
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index eedb5acc21ed..175b7eb42b0b 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -14,6 +14,7 @@ HAS_ADDRESS_AUTH_ARCH_QARMA5
 HAS_ADDRESS_AUTH_IMP_DEF
 HAS_AMU_EXTN
 HAS_ARMv8_4_TTL
+HAS_BBMLV2
 HAS_CACHE_DIC
 HAS_CACHE_IDC
 HAS_CNP
-- 
2.41.0