linux-kernel - Re: kdump failed because of hotplug memory adding in kdump kernel

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Message-ID: <20140109212705.GC12111@redhat.com>
Date:	Thu, 9 Jan 2014 16:27:05 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>, Baoquan <bhe@...hat.com>,
	linux-acpi@...r.kernel.org, zhangyanfei@...fujitsu.com,
	tangchen@...fujitsu.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, dyoung@...hat.com
Subject: Re: kdump failed because of hotplug memory adding in kdump kernel

On Thu, Jan 09, 2014 at 11:34:30AM -0700, Toshi Kani wrote:
> On Thu, 2014-01-09 at 13:23 -0500, Vivek Goyal wrote:
> > On Thu, Jan 09, 2014 at 10:24:25AM -0700, Toshi Kani wrote:
> > 
> > [..]
> > > > I think creating a new command line option is simpler as compared to
> > > > creating a new flag in bootparam which in turn disables memory hotplug.
> > > > More users can use that option. For example, if for some reason hotplug
> > > > code is crashing, one can just disable it on command line as work around
> > > > and move on.
> > > 
> > > I do not have a strong opinion about having such option.  However, I
> > > think it is more user friendly to keep the exactmap option works alone
> > > on any platforms.
> > 
> > I think we should create internally a variable which will disable memory
> > hotplug. And set that variable based on memmap=exactmap, mem=X and also
> > provide a way to disable memory hotplug directly using command line
> > option.
> > 
> > Current kexec-tools can use memmap=exactmap and be happy. I am writing
> > a new kexec syscall and will not be using memmap=exactmap and would need
> > to use that command line option to disable memory hotplug behavior.
> 
> Sounds good to me.

Nobody responded to my other question, so I would ask it again.

Assume we have disabled hotplug memory in second kernel. First kernel
saw hotplug memory and assume crash kernel reserved region came from
there. We will pass this memory in bootparams to second kernel and it
will show up in E820 map. It should still be accessible in second kernel,
is that right?

Or there is some dependency on ACPI doing some magic before this memory
range is available in second kernel?

Thanks
Vivek
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