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Call Depth Tracking with Linux 6.2 on Skylake cpu's


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Linux 6.2 Performance Option Helps Extend The Longevity Of Intel Skylake Era PCs



One of the new features introduced with Linux 6.2 is Call Depth Tracking and it can help extend the useful service life of Intel Skylake through Coffeelake era processors in providing better performance than is otherwise found out-of-the-box on Linux.



Call Depth Tracking was merged for Linux 6.2 and needs the "CALL_DEPTH_TRACKING" Kconfig build option enabled. Additionally, it's not used by default unless the "retbleed=stuff" option is passed to the kernel when booting the system.


Arch linux has the "CALL_DEPTH_TRACKING" Kconfig build option enabled. It shows up on my pc " Retbleed:Mitigation; IBRS ".


 Put brain in gear before pressing enter11:16:29-->Thu Feb 02-->~
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):                  8
  On-line CPU(s) list:   0-7
Vendor ID:               GenuineIntel
  Model name:            Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
  Itlb multihit:         KVM: Mitigation: VMX disabled
  L1tf:                  Mitigation; PTE Inversion; VMX conditional cache flushe
                         s, SMT vulnerable
  Mds:                   Mitigation; Clear CPU buffers; SMT vulnerable
  Meltdown:              Mitigation; PTI
  Mmio stale data:       Mitigation; Clear CPU buffers; SMT vulnerable
  Retbleed:              Mitigation; IBRS
  Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:            Mitigation; usercopy/swapgs barriers and __user pointer
  Spectre v2:            Mitigation; IBRS, IBPB conditional, RSB filling, PBRSB-
                         eIBRS Not affected


Am I correct in thinking that I can add " retbleed=stuff " to my boot loader like so ?



"Boot using default options" "root=PARTUUID=eb3de75a-01c4-4821-9de5-65d233f3154e  retbleed=stuff  rw initrd=intel-ucode.img  initrd=initramfs-%v.img"


More info on Retbleed



Edited by abarbarian
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On 2/2/2023 at 9:49 PM, securitybreach said:

Sorry, I have no clue but it might work. May as well try it..



Well as far as I can see it is a kernel boot option so I think I have it in the right place. Can not seem to find any information on how to test before and after to see if it does make a difference though. 😎

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