arm64: Add ARM64_HAS_LPA2 CPU capability

Expose FEAT_LPA2 as a capability so that we can take advantage of
alternatives patching in the hypervisor.

Although FEAT_LPA2 presence is advertised separately for stage1 and
stage2, the expectation is that in practice both stages will either
support or not support it. Therefore, we combine both into a single
capability, allowing us to simplify the implementation. KVM requires
support in both stages in order to use LPA2 since the same library is
used for hyp stage 1 and guest stage 2 pgtables.

Reviewed-by: Oliver Upton <[e-mail]>
Signed-off-by: Ryan Roberts <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm64/include/asm/cpufeature.h

···
 	return alternative_has_cap_unlikely(ARM64_HAS_TLB_RANGE);
 }
 
+static inline bool system_supports_lpa2(void)
+{
+	return cpus_have_final_cap(ARM64_HAS_LPA2);
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 

arch/arm64/kernel/cpufeature.c

···
 	return !meltdown_safe;
 }
 
+#if defined(ID_AA64MMFR0_EL1_TGRAN_LPA2) && defined(ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_LPA2)
+static bool has_lpa2_at_stage1(u64 mmfr0)
+{
+	unsigned int tgran;
+
+	tgran = cpuid_feature_extract_unsigned_field(mmfr0,
+					ID_AA64MMFR0_EL1_TGRAN_SHIFT);
+	return tgran == ID_AA64MMFR0_EL1_TGRAN_LPA2;
+}
+
+static bool has_lpa2_at_stage2(u64 mmfr0)
+{
+	unsigned int tgran;
+
+	tgran = cpuid_feature_extract_unsigned_field(mmfr0,
+					ID_AA64MMFR0_EL1_TGRAN_2_SHIFT);
+	return tgran == ID_AA64MMFR0_EL1_TGRAN_2_SUPPORTED_LPA2;
+}
+
+static bool has_lpa2(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	u64 mmfr0;
+
+	mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
+	return has_lpa2_at_stage1(mmfr0) && has_lpa2_at_stage2(mmfr0);
+}
+#else
+static bool has_lpa2(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 #define KPTI_NG_TEMP_VA		(-(1UL << PMD_SHIFT))
 
···
 		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
 		.matches = has_cpuid_feature,
 		ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, EVT, IMP)
+	},
+	{
+		.desc = "52-bit Virtual Addressing for KVM (LPA2)",
+		.capability = ARM64_HAS_LPA2,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_lpa2,
 	},
 	{},
 };

arch/arm64/tools/cpucaps

···
 HAS_GIC_PRIO_RELAXED_SYNC
 HAS_HCX
 HAS_LDAPR
+HAS_LPA2
 HAS_LSE_ATOMICS
 HAS_MOPS
 HAS_NESTED_VIRT