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In-Reply-To: <20180123170913.41791-5-kirill.shutemov@linux.intel.com>
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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 23 Jan 2018 09:31:16 -0800
Message-ID: <CA+55aFxgsZCqJdhZJ3ztyTTFPPgkn_aH6d4ziW1g0YJKc++0+A@mail.gmail.com>
Subject: Re: [PATCHv6, RESEND 4/4] x86/boot/compressed/64: Handle 5-level
 paging boot if kernel is above 4G
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Sender: owner-linux-mm@kvack.org
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, the arch/x86 maintainers <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@amacapital.net>, Cyrill Gorcunov <gorcunov@openvz.org>, Borislav Petkov <bp@suse.de>, Andi Kleen <ak@linux.intel.com>, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>

On Tue, Jan 23, 2018 at 9:09 AM, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> But if the bootloader put the kernel above 4G (not sure if anybody does
> this), we would lose control as soon as paging is disabled, because the
> code becomes unreachable to the CPU.

I do wonder if we need this. Why would a bootloader ever put the data
above 4G? Does this really happen?  Wouldn't it be easier to just say
"bootloaders better put the kernel in the low 4G"?

                Linus

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