arm64 crashkernel fails to boot on acpi-only machines due to ACPI regions being no longer mapped as NOMAP

[Dave Young]

On 12/26/17 at 08:26am, Bhupesh Sharma wrote:
> On Tue, Dec 26, 2017 at 7:58 AM, AKASHI Takahiro
> <takahiro.akashi at linaro.org> wrote:
> > On Tue, Dec 26, 2017 at 09:35:17AM +0800, Dave Young wrote:
> >> [snip]
> >> > > > Well, we may be able to change pr_warn() to pr_warn_once() here, but
> >> > > > I hope that adding "numa=off" to kernel command line should also work.
> >> > >
> >> > > Hmm, adding "numa=off" to crashkernel bootargs works, and TBH it was
> >> > > my initial thought process as well, but I am not sure if this will
> >> > > cause any regressions on aarch64 systems which use crashdump feature.
> >> >
> >> > It should be fine since we use numa=off by default for all other arches
> >> > ie. x86, ppc64 and s390. Actually disabling numa in kdump kernel can save
> >> > mm component memory usage.
> >> >
> >>
> >> Forgot to say I means in RHEL and Fedora we use numa=off for kdump..
> >
> > Thank you for the clarification.
> > (It might be better to make numa off automatically if maxcpus == 0 (and 1?).)
> >
> 
> Not sure if we can leave this to the distribution-specific kdump
> scripts (as the crashkernel boot can be held up for sufficient time
> and may appear stuck). The distribution scripts may be different (for
> e.g. ubuntu and RHEL/fedora) across distributions and may have
> different bootarg options.

Personally I think distribution should take care of this param as for
kdump.  But as AKASHI said it could be a issue for 1st kernel with
nr_cpus=1 booting.  Problem is why we do not see this issue on other
machines.

> 
> So how about considering a kernel fix only which doesn't require
> relying on changing the distribution-specific kdump scripts, as we
> should avoid introducing a regression while trying to fix a regression
> :)
> 
> Just my 2 cents.
> 
> Thanks,
> Bhupesh

Thanks
Dave