linux-kernel - Re: [PATCH v3 11/12] x86, boot: add fields to support load bzImage and ramdisk high

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Date:	Sat, 24 Nov 2012 21:52:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Rob Landley <rob@...dley.net>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v3 11/12] x86, boot: add fields to support load bzImage and ramdisk high

But it doesn't solve the bigger problem, and it is just begging to be gotten wrong.

Yinghai Lu <yinghai@...nel.org> wrote:

>On Sat, Nov 24, 2012 at 4:11 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> On Sat, Nov 24, 2012 at 4:04 PM, H. Peter Anvin <hpa@...or.com>
>wrote:
>>>
>>> It sounds like we are leaning toward some form of the sentinel hack,
>which
>>> means we need an enumerated list of things that should *not* be
>zeroed if
>>> the sentinel is present.
>>>
>>> The option of declaring the list frozen makes me a bit nervous,
>because it
>>> isn't clear that we don't already have fields that will be
>misinterpreted by
>>> the kernel if filled in from the file.
>>
>> USE_EXT_BOOT_PARAMS bit in xloadflags should work.
>
>new kexec will clean around bit around setup head, and set that bit,
>if it is not with real_mode entry.
>
>32bit and 64bit entry:
>old kernel has no idea of this bit, and still use old ramdisk_image,
>cmd_line_ptr in setup header.
>new kernel will check that bit before it use ext_ramdisk_image, and
>ext_cmd_line_ptr.
>
>old kexec and new kernel is safe too, because that bit is not set, new
>kernel will not use ex_...
>
>later all new kernel need to check USE_EXT_BOOT_PARAMS bit for all new
>added field in boot_params.

-- 
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