linux-kernel - Re: [PATCH 3/7] x86/mm/init: pass unconverted symbol addresses to free_init

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Date:   Sat, 4 Aug 2018 23:11:32 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jürgen Groß <jgross@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 3/7] x86/mm/init: pass unconverted symbol addresses to
 free_init_pages()

> [ Goes around and rummages ]
> 
> Oh, never mind, looking around reminded me why: we want to map the
> kernel text in the top 31 bits, so that we can use the faster
> -mcmodel=kernel because all symbols fit in sign-extended 32 bits.
> 
> Maybe there was some other reason too, but I think that's it.

No that was the only reason.

Large code model would be extremely expensive, and PIC linked
kernel also had some issues. So we ended up with this set up.

-Andi