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[EdLUG] Module parameters are different from cmdline

Edinburgh Linux Users Group edlug at lists.edlug.org.uk
Wed Dec 28 23:57:14 UTC 2016


Hi Roy,

After some investigation it turned out that Ubuntu packs both - gzipped
initrd.img and Intel's microcode into one initrd file. That's why I
couldn't initially extract the whole Init ramfs.

Now I see that i915.ko module is included into initrd and that
/etc/modprobe.d actually has i915.conf with my options inside. So, it's
clear now that i915 is a module and where its configuration comes from.
It's also confirmed by "dmesg" output where i915 reports setting of the
"dangerous options".

The weird thing now is - provided all of the facts above, the module still
ignores the config. It still continues to use some default settings.

There's no other place except /etc/modprobe.d in initrd which contains or
may override "enable_execlists" setting (checked by 'grepping' all of the
extracted contents)

Best Regards,
Maxim

On Wed, Dec 28, 2016 at 11:00 PM, Edinburgh Linux Users Group <
edlug at lists.edlug.org.uk> wrote:

> On 2016.12.28 21:12, Edinburgh Linux Users Group wrote:
> > Hi Roy,
> >
> > I see your point. Interesting, I see the entries from i915 (about
> > tainting
> > kernel) Before any root fs mounting. Which means that it's either
> > built
> > into the kernel or should be inside initramfs.
> >
> > Also, apart from the config, if I try to run this command:
> >
> > *$ grep i915 /lib/modules/4.8.0-32-generic/modules.builtin*
> > It gives no output, which means that i915 must be a separate module.
> >
> > However, when I try to look into initramfs:
> >
> > *$ cpio -i < initrd.img-4.8.0-32-generic*
> > I see only one file there:
> > *./kernel/x86/microcode/GenuineIntel.bin*
> >
> > Now I'm a bit confused - it's loaded before root fs, it's referred as
> > a
> > separate module in all configs, but it's not in initrd...
> >
> > Best Regards,
> > Maxim
> >
>
> Maxim,
>
> A few things.  I've put Ubuntu 16.10 into a Virtualbox VM beside
> a scrap Gentoo, so I can unpick the initramfs.
>
> Firstly. its init script parses /proc/cmdline so the init script
> in the initramfs can respond to kernel command line
> parameters.  It has lots defined already.  As you have
> the initrd unpacked its easy to read.
> I don't see it doing anything for i915 though.
>
> i915.ko is indeed in the initramfs. Look in it its
> lib/modules/.../kernel/drivers/gpu/drm ...
>
> I've had a look in the initramfs etc/m* and don't
> see anything passing parameters to i915 but I don't
> know my way around Ubuntu.
>
> Regards,
>
> Roy Bamford.
>
>
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> EdLUG at lists.edlug.org.uk
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>
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