linux-kernel - Re: [RFC/RFT PATCH 04/19] x86: Make the 64-bit bzImage always physically relocatable

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Message-ID: <3f2e8d7c-6029-49ef-8e31-a3eb5efb385b@zytor.com>
Date: Sun, 11 Jan 2026 20:01:02 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...nel.org>,
        Uros Bizjak <ubizjak@...il.com>, Brian Gerst <brgerst@...il.com>,
        linux-hardening@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 04/19] x86: Make the 64-bit bzImage always
 physically relocatable

On 2026-01-08 01:25, Ard Biesheuvel wrote:
> On x86_64, the physical placement of the kernel is independent from its
> mapping in the 'High Kernel Mapping' range. This means that even a
> position dependent kernel built without boot-time relocation support can
> run from any suitably aligned physical address, and there is no need to
> make this behavior dependent on whether or not the kernel is virtually
> relocatable.
> 
> On i386, the situation is different, given that the physical and virtual
> load offsets must be equal, and so only a relocatable kernel can be
> loaded at a physical address that deviates from its build-time default.
> 
> Clarify this in Kconfig and in the code, and advertise the 64-bit
> bzImage as loadable at any physical offset regardless of whether
> CONFIG_RELOCATABLE is set. In practice, this makes little difference,
> given that it defaults to 'y' and is a prerequisite for EFI_STUB and
> RANDOMIZE_BASE, but it will help with some future refactoring of the
> relocation code.
> 

I don't see any reason to support non-relocatable kernels anymore. In fact, in
a patchset I am working on I have already removed it.

	-hpa