Retpoline patch seems to have messed up kernel config

BarryK · 12-10-2018, 04:30 AM

The retpoline patch has been backported to the 4.14.* kernel, starting at 4.14.82. The problem is, when doing the "make menuconfig", retpoline can be disabled but SMT is forced on.

This is in "Processor type and features", you will see in there:

Code:

Processor type and features
  < > Avoid speculative indirect branches in kernel CONFIG_RETPOLINE
  [ ] SMT (hyperthreading) scheduler support CONFIG_SCHED_SMT

...the problem is, the SMT option has vanished, it is not there in the 4.14.87 kernel, and the SMT option is forced on. It is there in the 4.14.82 kernel.

I am wondering if this issue is showing up in later kernels?

Further info at blog post:

http://bkhome.org/news/201812/kernel...-compiled.html

business_kid · 12-10-2018, 06:31 AM

Why don't you grok the patch ported, (forward and back) and read the thread and inform yourself? I've had to do that occasionally. Linus doesn't bite anymore, I'm told. The DFL is gone and the BDFL is back

HMan81 · 12-15-2018, 02:38 PM

I have recently faced a similar issue when trying to build old code against kernel 4.19.6, in my case CONFIG_TRACEPOINTS was disabled and hidden... The fix is easy though. Edit init/Kconfig, find the line where your target is, and add a description after it. For example:

Code:

config CONFIG_SCHED_SMT
        bool

becomes

Code:

config CONFIG_SCHED_SMT
        bool "SMT (hyperthreading) scheduler support"

Save the file, go back in menuconfig, and look for your option, it should be visible again. Depending on how it was patched out it may or may not be in the same location in the menus, to find it use "/" in menuconfig.