Arch Linux

Vertennn

Member

Registered: 2024-11-10

Posts: 13

[SOLVED] Some CPUs are offline

I added mmio_stale_data=full,nosmt to the kernel parameters in /etc/default/grub to eliminate the "MMIO Stale Data CPU bug present and SMT on, data leak possible" error, and I noticed that since then, lscpu reports that cores 6-11 are offline. Is there a way to have all cores active and at the same time fix this vulnerability?

cat /proc/cmdline

BOOT_IMAGE=/vmlinuz-linux-zen root=/dev/mapper/volgroup0-lv_root rw quiet loglevel=0 mmio_stale_data=full,nosmt nosgx pcie_aspm=off

lscpu

Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          39 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   12
  On-line CPU(s) list:    0-5
  Off-line CPU(s) list:   6-11
Vendor ID:                GenuineIntel
  Model name:             Intel(R) Core(TM) i5-10400F CPU @ 2.90GHz
    CPU family:           6
    Model:                165
    Thread(s) per core:   1
    Core(s) per socket:   6
    Socket(s):            1
    Stepping:             3
    CPU(s) scaling MHz:   70%
    CPU max MHz:          4300.0000
    CPU min MHz:          0.0000
    BogoMIPS:             5799.77
    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 constant_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 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f
                          16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb ssbd ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid mpx rdseed adx 
                          smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp vnmi md_clear flush_l1d arch_capabilities
Virtualization features:  
  Virtualization:         VT-x
Caches (sum of all):      
  L1d:                    192 KiB (6 instances)
  L1i:                    192 KiB (6 instances)
  L2:                     1.5 MiB (6 instances)
  L3:                     12 MiB (1 instance)
NUMA:                     
  NUMA node(s):           1
  NUMA node0 CPU(s):      0-5
Vulnerabilities:          
  Gather data sampling:   Mitigation; Microcode
  Itlb multihit:          KVM: Mitigation: VMX disabled
  L1tf:                   Not affected
  Mds:                    Not affected
  Meltdown:               Not affected
  Mmio stale data:        Mitigation; Clear CPU buffers; SMT disabled
  Reg file data sampling: Not affected
  Retbleed:               Mitigation; Enhanced IBRS
  Spec rstack overflow:   Not affected
  Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Spectre v2:             Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB filling; PBRSB-eIBRS SW sequence; BHI SW loop, KVM SW loop
  Srbds:                  Mitigation; Microcode
  Tsx async abort:        Not affected

Last edited by Vertennn (2024-11-10 16:28:25)

ua4000

Member

Registered: 2015-10-14

Posts: 485

Re: [SOLVED] Some CPUs are offline

Your cpu has only 6 real physical cpu cores, the other 6 are from Hyper-Threading  / SMT - so the outcome of option "nosmt" is expected like this.
I don't know, if your 4 year's old cpu can be fixed otherwise.
You are are using
https://wiki.archlinux.org/title/Microcode
already ? Mabye after using it, "nosmt" may be not required anymore ?

Vertennn

Member

Registered: 2024-11-10

Posts: 13

Re: [SOLVED] Some CPUs are offline

Yes, I have installed intel-ucode.

dmesg | grep microcode

[    0.360035] microcode: Current revision: 0x000000fc
[    0.360037] microcode: Updated early from: 0x000000f6
[    0.360054] mce: [Hardware Error]: PROCESSOR 0:a0653 TIME 1731251718 SOCKET 0 APIC 0 microcode fc

loqs

Member

Registered: 2014-03-06

Posts: 18,042

Re: [SOLVED] Some CPUs are offline

Do you run untrusted code or virtual machines on the affected system which could exploit the vulnerability?

Vertennn

Member

Registered: 2024-11-10

Posts: 13

Re: [SOLVED] Some CPUs are offline

I do not run it. So, what do you suggest I should do? On one hand, it would be good if the vulnerability stays fixed, but on the other hand, I care about performance.

Last edited by Vertennn (2024-11-10 15:49:09)

loqs

Member

Registered: 2014-03-06

Posts: 18,042

Re: [SOLVED] Some CPUs are offline

I would use upstream kernels default mitigation which I believe is equivalent to mmio_stale_data=full leaving SMT vulnerable unless I have reason to believe that vulnerability is going to be exploited.

Vertennn

Member

Registered: 2024-11-10

Posts: 13

Re: [SOLVED] Some CPUs are offline

Alright, I think I'll do that. Thanks for your time