[Bug 1911959] Re: Fresh Ubuntu 20.04 won't boot after intel-microcode update on ThinkPad T460s

[Markus Konrad]

I can confirm that downgrading intel-microcode to version
"3.20191115.1ubuntu3" resolves the issue. I've marked the package as "on
hold" for now.

Here's my "lscpu" output that I forgot in my initial report:

Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   39 bits physical, 48 bits virtual
CPU(s):                          4
On-line CPU(s) list:             0-3
Thread(s) per core:              2
Core(s) per socket:              2
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                           78
Model name:                      Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz
Stepping:                        3
CPU MHz:                         799.864
CPU max MHz:                     3400.0000
CPU min MHz:                     400.0000
BogoMIPS:                        5599.85
Virtualization:                  VT-x
L1d cache:                       64 KiB
L1i cache:                       64 KiB
L2 cache:                        512 KiB
L3 cache:                        4 MiB
NUMA node0 CPU(s):               0-3
Vulnerability Itlb multihit:     KVM: Mitigation: VMX disabled
Vulnerability L1tf:              Mitigation; PTE Inversion; VMX conditional cache flushes, SMT vulnerable
Vulnerability Mds:               Mitigation; Clear CPU buffers; SMT vulnerable
Vulnerability Meltdown:          Mitigation; PTI
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, IBPB conditional, IBRS_FW, STIBP conditional, RSB f
                                 illing
Vulnerability Srbds:             Vulnerable: No microcode
Vulnerability Tsx async abort:   Mitigation; Clear CPU buffers; SMT vulnerable
Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acp
                                 i mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_per
                                 fmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64
                                  monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic
                                  movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cp
                                 uid_fault epb invpcid_single pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept 
                                 vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx
                                  smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hw
                                 p_notify hwp_act_window hwp_epp md_clear flush_l1d

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https://bugs.launchpad.net/bugs/1911959

Title:
  Fresh Ubuntu 20.04 won't boot after intel-microcode update on ThinkPad
  T460s

Status in intel-microcode package in Ubuntu:
  Confirmed

Bug description:
  Installed Ubuntu 20.04 from USB disk using the first Ubuntu 20.04
  installation image released end of April. The system installs and
  boots fine. Then, I run a system update via `apt update && apt
  upgrade` with updates to Ubuntu 20.04.1. intel-microcode is updated on
  this occasion to version 3.20201110.0ubuntu0.20.04.2. Update
  installation succeeds but subsequent reboots most of the time fail. I
  can access GRUB but a normal boot of any of the installed kernels
  results in either a black screen or a screen with a cursor blinking ad
  infinitum. Booting in recovery mode via GRUB and then "resume" works,
  but external display is not detected in this case. Sometimes however
  (maybe 1/5 of the time), making a reboot from this state works.

  When I uninstall intel-microcode via `apt purge intel-microcode` the
  problems disappear. I can boot the system without any problem.

  I had occasional boot problems already since several months, but they
  could be resolved by just rebooting (pressing the power key for a long
  time). After the latest update, this wouldn't work anymore, so in the
  end I tried out re-installing Ubuntu which resulted in the problems
  described above.

  I'm using a Lenovo ThinkPad T460s with system firmware version
  N1CET37W (1.05) which is quite old.

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