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From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 28 Mar 2017 15:55:47 -0700
Message-ID: <CALCETrVnc6pWKcbFWeJHmPVDtmD5Js_LbW_AVbx-sBJ0hpRNwQ@mail.gmail.com>
Subject: Re: [PATCH] x86/boot: Support uncompressed kernel
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Chao Peng <chao.p.peng@linux.intel.com>, Arnd Bergmann <arnd@arndb.de>,
        Michal Marek <mmarek@suse.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Yinghai Lu <yinghai@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Kees Cook <keescook@chromium.org>, Baoquan He <bhe@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Paul Bolle <pebolle@tiscali.nl>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Borislav Petkov <bp@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        "David S. Miller" <davem@davemloft.net>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Garnier <thgarnie@google.com>,
        Nicolas Pitre <nicolas.pitre@linaro.org>, Tejun Heo <tj@kernel.org>,
        Daniel Mack <daniel@zonque.org>, Helge Deller <deller@gmx.de>,
        Rik van Riel <riel@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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On Tue, Mar 28, 2017 at 3:38 PM, H. Peter Anvin <hpa@zytor.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.