Frequent freezes loading initial ramdisk...

首先使用报告中的 kernel 命令参数在 Asus N752VX 上重现 freeze，并比较有无 intel-ucode 时的启动情况。检查 linux、linux-zen 和 linux-lts 各版本中 con_init、tty0 和 efifb0 附近的最后几条消息。完成的标准是确定 kernel/microcode 的交互，并记录一个经过验证的 fix 或 workaround；未指定源文件或测试。

When I reboot or power on my Asus N752VX laptop with Archlinux, it often freezes at an early boot stage.
When I'm using GRUB it freezes displaying "Loading initial ramdisk ...".
Adding " initcall_debug earlycon=efifb" to the kernel command, the last kernel messages displayed when it freezes are:

calling con_init+0x0/0x25e @ 0
Console: colour dummy device 80x25
printk: console [tty0] enabled
printk: bootconsole [efifb0] disabled"

When the freeze happens the cpu fan starts running at maximum speed and I can only force a shutdown pressing the laptop power button.

This issue is present in all linux, linux-zen and linux-lts since some months.
The only way to workaround it is by avoiding to load the intel-ucode (version 20210216-1)

Reverting back to previous versions of intel-ucode (up to 20190918) did not solve the issue, so it seems an interaction between newer kernels (5.10 and following ones) and intel-ucode.

Reverting to previous kernel is pretty impossible on a rolling release like Archlinux.

Steps to reproduce:
Reboot the PC until the problem occurs. Typically less than 4 rebooting are sufficient.

lscpu:
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): 8
On-line CPU(s) list: 0-3
Off-line CPU(s) list: 4-7
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 94
Model name: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
Stepping: 3
CPU MHz: 800.044
CPU max MHz: 3500,0000
CPU min MHz: 800,0000
BogoMIPS: 5199.98
Virtualization: VT-x
L1d cache: 128 KiB
L1i cache: 128 KiB
L2 cache: 1 MiB
L3 cache: 6 MiB
NUMA node0 CPU(s): 0-3
Vulnerability Itlb multihit: KVM: Mitigation: VMX disabled
Vulnerability L1tf: Mitigation; PTE Inversion; VMX conditional cache flushes, SMT disabled
Vulnerability Mds: Mitigation; Clear CPU buffers; SMT disabled
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, RSB filling
Vulnerability Srbds: Mitigation; Microcode
Vulnerability Tsx async abort: Mitigation; Clear CPU buffers; SMT disabled
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constan
t_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 sdbg fma cx16 xtp
r pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_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 in
tel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp md_clear flush_l1d