linux-kernel - Re: [PATCH] x86/boot: Support uncompressed kernel

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Message-ID: <CALCETrVnc6pWKcbFWeJHmPVDtmD5Js_LbW_AVbx-sBJ0hpRNwQ@mail.gmail.com>
Date:   Tue, 28 Mar 2017 15:55:47 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, Michal Marek <mmarek@...e.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Yinghai Lu <yinghai@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>, Baoquan He <bhe@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Paul Bolle <pebolle@...cali.nl>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Borislav Petkov <bp@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Tejun Heo <tj@...nel.org>, Daniel Mack <daniel@...que.org>,
        Helge Deller <deller@....de>, Rik van Riel <riel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] x86/boot: Support uncompressed kernel

On Tue, Mar 28, 2017 at 3:38 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 03/28/17 05:01, Chao Peng wrote:
>>>
>>> I guess the next step would be to use CONFIG_XIP_KERNEL on x86,
>>> which requires an uncompressed kernel but has the additional advantage
>>> of sharing the read-only sections of the kernel image across virtual
>>> machines, resulting in better RAM and cache usage.
>>
>> That is something we wanna look into :)
>>
>
> It is, but that is a second order thing... especially since the x86
> kernel makes heavy use of self-patching at the moment.  What would be
> more significant, though, would be to avoid the memcpy() and instead
> decode the uncompressed kernel in-place.
>

Having looked at this code recently, I'd rather fix it differently:
use the streaming decompression API and integrate it with the ELF
parsing code so we can decompress directly into the actual load
location.  Also, the parse_elf() code needs some serious improved
documentation and robustification.  It's absurdly fragile right now.