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SubjectRe: [PATCH v5] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode
+ Masami.

On Thu, Jul 09, 2020 at 12:51:34PM +0200, Thomas Gleixner wrote:
> Abhishek Bhardwaj <> writes:
> > This change adds a new kernel configuration that sets the l1d cache
> > flush setting at compile time rather than at run time.
> >
> > The reasons for this change are as follows -
> >
> > - Kernel command line arguments are getting unwieldy. These parameters
> > are not a scalable way to set the kernel config. They're intended as a
> > super limited way for the bootloader to pass info to the kernel and
> > also as a way for end users who are not compiling the kernel themselves
> > to tweak the kernel behavior.
> >
> > - Also, if a user wants this setting from the start. It's a definite
> > smell that it deserves to be a compile time thing rather than adding
> > extra code plus whatever miniscule time at runtime to pass an
> > extra argument.
> >
> > - Finally, it doesn't preclude the runtime / kernel command line way.
> > Users are free to use those as well.
> TBH, I don't see why this is a good idea.
> 1) I'm not following your argumentation that the command line option is
> a poor Kconfig replacement. The L1TF mode is a boot time (module
> load time) decision and the command line parameter is there to
> override the carefully chosen and sensible default behaviour.
> 2) You can add the desired mode to the compiled in (partial) kernel
> command line today.
> 3) Boot loaders are well capable of handling large kernel command lines
> and the extra time spend for reading the parameter does not matter
> at all.

Also, there's Documentation/admin-guide/bootconfig.rst which extends
cmdline options handling even more and allows for passing options in a
file. Maybe that'll help in this case too.


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