arm64: Use register field helper in kaslr_requires_kpti()

Rather than open-code the extraction of the E0PD field from the MMFR2
register, we can use the cpuid_feature_extract_unsigned_field() helper
instead.

Acked-by: Suzuki K Poulose <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

Author: willdeacon

arch/arm64/kernel/cpufeature.c

@@ -980,7 +980,6 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
  */
 bool kaslr_requires_kpti(void)
 {
-	u64 ftr;
 	if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
 		return false;
 
@@ -989,8 +988,9 @@ bool kaslr_requires_kpti(void)
 	 * where available.
 	 */
 	if (IS_ENABLED(CONFIG_ARM64_E0PD)) {
-		ftr = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
-		if ((ftr >> ID_AA64MMFR2_E0PD_SHIFT) & 0xf)
+		u64 mmfr2 = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
+		if (cpuid_feature_extract_unsigned_field(mmfr2,
+						ID_AA64MMFR2_E0PD_SHIFT))
 			return false;
 	}