[PATCH RFC v9 16/25] arm64: kpkeys: Implement arch_supports_kpkeys_early()

[Kevin Brodsky]

We need to check if the kpkeys_hardened_pgtables feature is going to
be enabled very early during boot, to decide how to set up the
linear map and how to allocate early page tables. This happens even
before boot CPU features are detected.

Implement the arch_supports_kpkeys_early() helper by directly
checking if the boot CPU supports POE, if it is called before boot
CPU features are detected. It may also be called later, in which
case we simply check the POE feature.

Signed-off-by: Kevin Brodsky <kevin.brodsky at arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 12 ++++++++++++
 arch/arm64/include/asm/kpkeys.h     |  7 +++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a57870fa96db..37aae60c2d7f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -1085,6 +1085,18 @@ static inline bool cpu_has_lpa2(void)
 #endif
 }
 
+static inline bool cpu_has_poe(void)
+{
+	u64 mmfr3;
+
+	if (!IS_ENABLED(CONFIG_ARM64_POE))
+		return false;
+
+	mmfr3 = read_sysreg_s(SYS_ID_AA64MMFR3_EL1);
+	return cpuid_feature_extract_unsigned_field(mmfr3,
+						    ID_AA64MMFR3_EL1_S1POE_SHIFT);
+}
+
 #endif /* __ASSEMBLER__ */
 
 #endif
diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index 09fd5a849cb0..284039e9a244 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -21,6 +21,13 @@ static inline bool arch_supports_kpkeys(void)
 	return system_supports_poe();
 }
 
+static inline bool arch_supports_kpkeys_early(void)
+{
+	/* POE is a boot feature */
+	return boot_capabilities_finalized() ?
+		system_supports_poe() : cpu_has_poe();
+}
+
 #ifdef CONFIG_ARM64_POE
 
 static inline u64 por_set_kpkeys_context(u64 por, enum kpkeys_ctx ctx)

-- 
2.51.2