static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
        int scope)
{
  …………
  /* Useful for KASLR robustness */
  if (kaslr_requires_kpti()) {
    if (!__kpti_forced) {
      str = "KASLR";
      __kpti_forced = 1;
    }
  }
  …………
  /* Forced? */
  if (__kpti_forced) {
    pr_info_once("kernel page table isolation forced %s by %s\n",
           __kpti_forced > 0 ? "ON" : "OFF", str);
    return __kpti_forced > 0;
  }
  …………
}

/*
 * This check is triggered during the early boot before the cpufeature
 * is initialised. Checking the status on the local CPU allows the boot
 * CPU to detect the need for non-global mappings and thus avoiding a
 * pagetable re-write after all the CPUs are booted. This check will be
 * anyway run on individual CPUs, allowing us to get the consistent
 * state once the SMP CPUs are up and thus make the switch to non-global
 * mappings if required.
 */
bool kaslr_requires_kpti(void)
{
  if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
    return false;
  /*
   * E0PD does a similar job to KPTI so can be used instead
   * where available.
   */
  if (IS_ENABLED(CONFIG_ARM64_E0PD)) {
    u64 mmfr2 = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
    if (cpuid_feature_extract_unsigned_field(mmfr2,
            ID_AA64MMFR2_E0PD_SHIFT))
      return false;
  }
  /*
   * Systems affected by Cavium erratum 24756 are incompatible
   * with KPTI.
   */
  if (IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456)) {
    extern const struct midr_range cavium_erratum_27456_cpus[];
    if (is_midr_in_range_list(read_cpuid_id(),
            cavium_erratum_27456_cpus))
      return false;
  }
  return kaslr_offset() > 0;
}

CONFIG_ARM64_E0PD=y