linux-kernel - Re: [PATCH] crash_core: Fix the check for whether crashkernel is from high memory

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Date:   Mon, 11 Dec 2023 13:53:12 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Yuntao Wang <ytcoode@...il.com>, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Zhen Lei <thunder.leizhen@...wei.com>
Subject: Re: [PATCH] crash_core: Fix the check for whether crashkernel is
 from high memory

On 12/09/23 at 02:34pm, Andrew Morton wrote:
> On Sat,  9 Dec 2023 22:14:38 +0800 Yuntao Wang <ytcoode@...il.com> wrote:
> 
> > If crash_base is equal to CRASH_ADDR_LOW_MAX, it also indicates that
> > the crashkernel memory is allocated from high memory. However, the
> > current check only considers the case where crash_base is greater than
> > CRASH_ADDR_LOW_MAX. Fix it.
> > 
> > This patch also includes some minor cleanups.
> 
> Can we please include a description of the runtime effects of this
> change?  ie, what happens now and under what circumstances, and how
> does the fix alter these things?

This is a good catch. Guess it's observed from code exploring.

The runtime effects is that crashkernel high memory is successfully
reserved, whereas the crashkernel low memory is bypassed in this
case, then kdump kernel bootup will fail because of no low memory
under 4G.