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

From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	kexec@lists.infradead.org, James Morse <james.morse@arm.com>,
	Bhupesh SHARMA <bhupesh.linux@gmail.com>,
	Dave Young <dyoung@redhat.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: arm64 crashkernel fails to boot on acpi-only machines due to ACPI regions being no longer mapped as NOMAP
Date: Tue, 9 Jan 2018 13:42:53 +0900	[thread overview]
Message-ID: <20180109030717.GA18820@linaro.org> (raw)
In-Reply-To: <CACi5LpNeSNHoUcM9xOq0bjN_okaEUDbaz1qyuqAct7BSNLQqKQ@mail.gmail.com>

Bhupesh,

On Tue, Jan 09, 2018 at 01:30:07AM +0530, Bhupesh Sharma wrote:
> Hello Akashi,
> 
> On Tue, Dec 26, 2017 at 8:26 AM, Bhupesh Sharma <bhsharma@redhat.com> wrote:
> > On Tue, Dec 26, 2017 at 7:58 AM, AKASHI Takahiro
> > <takahiro.akashi@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.
> >
> > 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.
> >
> 
> Sorry for the delay but I was on holidays in the last week.
> 
> Are you planning to send a patch to fix this issue or do you want me
> to send a RFC version instead?

I should have submitted my own patch before my new year holidays,
but I will do so as soon as possible.

Thanks,
-Takahiro AKASHI

> i think this is a blocking issue for aarch64 kdump support on newer
> kernels (v4.14) and we are already hearing about this issue from other
> users as well, so it would be great to get this fixed now that we have
> root-caused the issue and found a possible way around.
> 
> Regards,
> Bhupesh

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