IBRS не включен

На моем компьютере с Ubuntu 16.04 проверка-расплавления спектров выдает следующее:

Spectre and Meltdown mitigation detection tool v0.37+

Checking for vulnerabilities on current system
Kernel is Linux 4.4.0-122-generic #146-Ubuntu SMP Mon Apr 23 15:34:04 UTC 2018 x86_64
CPU is Intel(R) Celeron(R) CPU  N3150  @ 1.60GHz

Hardware check
* Hardware support (CPU microcode) for mitigation techniques
  * Indirect Branch Restricted Speculation (IBRS)
    * SPEC_CTRL MSR is available:  YES 
    * CPU indicates IBRS capability:  YES  (SPEC_CTRL feature bit)
  * Indirect Branch Prediction Barrier (IBPB)
    * PRED_CMD MSR is available:  YES 
    * CPU indicates IBPB capability:  YES  (SPEC_CTRL feature bit)
  * Single Thread Indirect Branch Predictors (STIBP)
    * SPEC_CTRL MSR is available:  YES 
    * CPU indicates STIBP capability:  YES  (Intel STIBP feature bit)
  * Enhanced IBRS (IBRS_ALL)
    * CPU indicates ARCH_CAPABILITIES MSR availability:  NO 
    * ARCH_CAPABILITIES MSR advertises IBRS_ALL capability:  NO 
  * CPU explicitly indicates not being vulnerable to Meltdown (RDCL_NO):  NO 
  * CPU microcode is known to cause stability problems:  NO  (model 76 stepping 3 ucode 0x367 cpuid 0x406c3)
* CPU vulnerability to the three speculative execution attack variants
  * Vulnerable to Variant 1:  YES 
  * Vulnerable to Variant 2:  YES 
  * Vulnerable to Variant 3:  YES 

CVE-2017-5753 [bounds check bypass] aka 'Spectre Variant 1'
* Mitigated according to the /sys interface:  YES  (Mitigation: OSB (observable speculation barrier, Intel v6))
* Kernel has array_index_mask_nospec (x86):  NO 
* Kernel has the Red Hat/Ubuntu patch:  YES 
* Kernel has mask_nospec64 (arm):  NO 
> STATUS:  NOT VULNERABLE  (Mitigation: OSB (observable speculation barrier, Intel v6))

CVE-2017-5715 [branch target injection] aka 'Spectre Variant 2'
* Mitigated according to the /sys interface:  YES  (Mitigation: Full generic retpoline, IBPB (Intel v4))
* Mitigation 1
  * Kernel is compiled with IBRS support:  YES 
    * IBRS enabled and active:  YES  (for both kernel and user space)
  * Kernel is compiled with IBPB support:  YES 
    * IBPB enabled and active:  YES 
* Mitigation 2
  * Kernel has branch predictor hardening (arm):  NO 
  * Kernel compiled with retpoline option:  YES 
    * Kernel compiled with a retpoline-aware compiler:  YES  (kernel reports full retpoline compilation)
> STATUS:  NOT VULNERABLE  (Full retpoline + IBPB are mitigating the vulnerability)

CVE-2017-5754 [rogue data cache load] aka 'Meltdown' aka 'Variant 3'
* Mitigated according to the /sys interface:  YES  (Mitigation: PTI)
* Kernel supports Page Table Isolation (PTI):  YES 
  * PTI enabled and active:  YES 
  * Reduced performance impact of PTI:  NO  (PCID/INVPCID not supported, performance impact of PTI will be significant)
* Running as a Xen PV DomU:  NO 
> STATUS:  NOT VULNERABLE  (Mitigation: PTI)

A false sense of security is worse than no security at all, see --disclaimer

Обновление микрокода поддерживает IBRS, но не включено по умолчанию (но может быть включено, см. Ответ). Вместо ретполина с IBPB используется для смягчения. Почему это так? Будет ли IBRS не лучшей защитой, как ретполин, потому что IBRS защищает также пространство пользователя? Как я могу заставить ядро ​​использовать IBRS?