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Date: Sat, 24 Nov 2012 21:50:01 -0800
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Subject: Re: [PATCH v3 11/12] x86, boot: add fields to support load bzImage
 and ramdisk high
From: Yinghai Lu <yinghai@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org, Rob Landley <rob@landley.net>,
        Matt Fleming <matt.fleming@intel.com>
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On Sat, Nov 24, 2012 at 4:11 PM, Yinghai Lu <yinghai@kernel.org> wrote:
> On Sat, Nov 24, 2012 at 4:04 PM, H. Peter Anvin <hpa@zytor.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.