Add "dis_ucode_ldr" to linux boot options for Recovery Mode

[Tyler Hicks]

On 2019-06-05 20:00:54, Jeroen Bobbeldijk wrote:
> Thanks. I'll open a report for grub2.
> According to the docs, dis_ucode_ldr is x86 only
> (arch/x86/kernel/cpu/microcode/core.c), so my guess is that it will be
> ignored for other architectures. According to the kernel code,
> dis_ucode_ldr works for both AMD and Intel.

Agreed on all the above.

For anyone else following along, Jeroen opened the following bug report:

 https://launchpad.net/bugs/1831789

> I have some time tomorrow on test this on a ARM device.

After taking a look at the grub2 code, it looks like it'll be easy
enough to only inject the dis_ucode_ldr option on x86. There's no need
to test that option on other architectures at this time. Thanks for the
offer, though.

Tyler

> 
> Jeroen
> 
> On Wed, Jun 5, 2019 at 7:49 PM Tyler Hicks <tyhicks at canonical.com> wrote:
> 
> > On 2019-06-05 10:03:06, Jeroen Bobbeldijk wrote:
> > > Hi,
> > >
> > > Due to some recent problems with a microcode update which broke booting
> > of
> > > some laptops I suggest adding "dis_ucode_ldr" to recovery mode boot
> > options
> > > to allow booting after a bad microcode update.
> > >
> > > See the following topics that describe the problems:
> > >  - https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1829620
> > >  -
> > https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/1
> > >
> > > When such problems occur it's very hard to see that the microcode loading
> > > is the issue, the booting just hangs at the purple screen, even removing
> > > "quiet splash" will not show the error.
> >
> > I really like this idea. Thanks for mentioning it.
> >
> > Please open a bug report here:
> >
> >  https://bugs.launchpad.net/ubuntu/+source/grub2/+filebug
> >
> > We'll need to double check that dis_ucode_ldr works as expected across
> > all architectures. Otherwise, I can't think of any other technical
> > blockers to doing this.
> >
> > Tyler
> >
> > >
> > > Kind regards,
> > >
> > > Jeroen
> >
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> >