linux-kernel - Re: [PATCH v6 18/27] x86, boot: add fields to support load bzImage and ramdisk above 4G

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Message-ID: <50CA66F0.50804@zytor.com>
Date:	Thu, 13 Dec 2012 15:38:24 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v6 18/27] x86, boot: add fields to support load bzImage
 and ramdisk above 4G

On 12/13/2012 03:28 PM, Yinghai Lu wrote:
> On Thu, Dec 13, 2012 at 2:54 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> 0x1f0 is unsuitable for use as sentinel -- or in fact for any purpose --
>> because it is quite plausible that someone may (fairly sanely) start the
>> copy range at 0x1f0 instead of 0x1f1... we really should have documented
>> it that way but it is too late now.
>>
>> However, we can use 0x1ef.
>
> right. updated to use 0x1ef.
>

> +1EF/001	ALL	sentinel	0: states _ext_* fields are valid

Not the correct documentation.  What this does is detect broken 
32/64-bit bootloaders, and the remediation code should zero not just the 
ext_* fields but all the fields that were identified as uninitialized -- 
we're kind of assuming that kexec is representative here, since it 
doesn't help us by giving an ID.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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