linux-kernel - Re: kdump broken on 2.6.37-rc4

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Message-ID: <20101217201104.GG14502@redhat.com>
Date:	Fri, 17 Dec 2010 15:11:04 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On Fri, Dec 17, 2010 at 11:56:23AM -0800, H. Peter Anvin wrote:
> On 12/17/2010 11:50 AM, Vivek Goyal wrote:
> > On Fri, Dec 17, 2010 at 11:46:08AM -0800, Yinghai Lu wrote:
> >> On 12/17/2010 11:39 AM, H. Peter Anvin wrote:
> >>> On 12/17/2010 10:21 AM, Yinghai Lu wrote:
> >>>>>>
> >>>>>> Do we have actual testing for how high the 64-bit kernel will load?
> >>>>>
> >>>>> I will do some experiments on my box today and let you know.
> >>>>
> >>>> if bzImage is used, it is 896M.
> >>>>
> >>>
> >>> Why?  896 MiB is a 32-bit kernel limitation which doesn't have anything
> >>> to do with the bzImage format.
> >>>
> >>> So unless there is something going on here, I suspect you're just plain
> >>> flat wrong.
> >>
> >> kexec-tools have some checking when it loads bzImage.
> >>
> > 
> > Yinghai,
> > 
> > I think x86_64 might have just inherited the settings of 32bit without
> > giving it too much of thought. At that point of time nobody bothered
> > to load the kernel from high addresses. So these might be artificial
> > limits.
> > 
> 
> Can we do this in the meantime, just so we fix the immediate problem?

Peter, kexec-tools on 64bit currently seems to be allowing loding bzImage
till 896MB. So I am not too keen it to reduce it to 768MB in kernel just
because x86_64 could be booted from even higher addresses and somebody
first has to do some auditing and experiments.

IMHO, we should have 768MB limit for 32bit and continue with 896MB limit for
64bit and once somebody makes x86_64 boot from even higher address reliably
then we can change both kernel and kexec-tools.

Thanks
Vivek
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