linux-kernel - Re: [PATCH 5/6] kexec-bzImage: Support for loading bzImage using 64bit entry

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Message-ID: <528F7735.9010209@zytor.com>
Date:	Fri, 22 Nov 2013 07:24:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivek Goyal <vgoyal@...hat.com>, Greg KH <greg@...ah.com>
CC:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, mjg59@...f.ucam.org
Subject: Re: [PATCH 5/6] kexec-bzImage: Support for loading bzImage using
 64bit entry

On 11/21/2013 11:21 AM, Vivek Goyal wrote:
>>
>> What do you mean by the "real mode entry"?  Do we need to care about
>> that because we aren't falling back to real mode when executing this,
>> are we?  Or does that just happen for 32bit kernels?
> 
> Original kexec offers real mode entry choice too. So we fall back
> to real mode and jump to kernel and kernel makes bunch of BIOS calls. I
> don't think this is a commonly used option.
> 

I know some users of it (who I shall not name.)  In general it is a bad
option, because after running the first kernel the state of the hardware
is not guaranteed to be such that executing the BIOS is safe.  In
general, I do think they do it just because they tried at some point and
it happened to work; discouraging its use is probably for the better.

	-hpa

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