Re: Linux/i386 boot protocol version 2.03

From: H. Peter Anvin (
Date: Sun Dec 09 2001 - 16:53:12 EST

Eric W. Biederman wrote:
> A couple of notes:
> 1) The minimum safe ramdisk address is 8MB (since 2.4.10). On low
> mem machines you can get away with placing a ramdisk lower. But we
> don't do any checking in our initial 8MB memory map.
> 2) If we use units of kilobytes instead of bytes for this we don't
> loose any precision and gain the ability to put a ramdisk in high
> memory without bumping the protocol version.
> 3) If we are going to export the maximum address we should also export
> the minimum address.

(2) I guess I'm not so concerned with the ramdisk in highmem since it is
extrememly unlikely any boot loader will be able to take advantage of
that. It could be an issue for x86-64, I guess.

(3) Contradicts (1) as well as issues with older kernels. Keep in mind
what happens if you violate this limit: the bootloader should be loading
the initrd as high as possible, so the only difference is if you get the
error message from the boot loader or from the kernel later. If you're
going to export a limit, you better make sure it's right; "8MB except on
low memory configurations" doesn't cut it. It's exactly on those low
memory configurations that this limit matters *at all*.


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