linux-kernel - Re: [PATCH v17 02/10] x86: kdump: make the lower bound of crash kernel reservation consistent

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Message-ID: <YbjvXl51hc6GZa71@arm.com>
Date:   Tue, 14 Dec 2021 19:24:14 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>
Subject: Re: [PATCH v17 02/10] x86: kdump: make the lower bound of crash
 kernel reservation consistent

On Tue, Dec 14, 2021 at 08:07:58PM +0100, Borislav Petkov wrote:
> On Fri, Dec 10, 2021 at 02:55:25PM +0800, Zhen Lei wrote:
> > From: Chen Zhou <chenzhou10@...wei.com>
> > 
> > The lower bounds of crash kernel reservation and crash kernel low
> > reservation are different, use the consistent value CRASH_ALIGN.
> 
> A big WHY is missing here to explain why the lower bound of the
> allocation range needs to be 16M and why was 0 wrong?

I asked the same here:

https://lore.kernel.org/r/20210224143547.GB28965@arm.com

IIRC Baoquan said that there is a 1MB reserved for x86 anyway in the
lower part, so that's equivalent in practice to starting from
CRASH_ALIGN.

Anyway, I agree the commit log should describe this.

-- 
Catalin