linux-kernel - Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING

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Message-ID: <20170316081429.GA28585@gmail.com>
Date:   Thu, 16 Mar 2017 09:14:29 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Baoquan He <bhe@...hat.com>, tglx@...utronix.de, hpa@...or.com,
        mingo@...hat.com, linux-kernel@...r.kernel.org, x86@...nel.org,
        keescook@...omium.org, yinghai@...nel.org, anderson@...hat.com,
        luto@...nel.org, thgarnie@...gle.com, kuleshovmail@...il.com
Subject: Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING_SIZE


* Borislav Petkov <bp@...e.de> wrote:

> Ok,
> 
> TBH, I still don't like adding yet another define and paying attention
> to whether I should use image size or mapping size. After your patch,
> KERNEL_IMAGE_SIZE is used to enforce the actual image size from
> exploding:
> 
> arch/x86/include/asm/page_32_types.h:43:#define KERNEL_IMAGE_SIZE       (512 * 1024 * 1024)
> arch/x86/include/asm/page_32_types.h:49:#define KERNEL_MAPPING_SIZE     KERNEL_IMAGE_SIZE
> arch/x86/include/asm/page_64_types.h:56:#define KERNEL_IMAGE_SIZE       (512 * 1024 * 1024)
> arch/x86/include/asm/pgtable_32.h:83: *     (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
> arch/x86/include/asm/pgtable_32.h:84: *     (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
> arch/x86/include/asm/pgtable_32.h:91: * KERNEL_IMAGE_SIZE should be greater than pa(_end)
> arch/x86/kernel/vmlinux.lds.S:356:. = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
> arch/x86/kernel/vmlinux.lds.S:357:         "kernel image bigger than KERNEL_IMAGE_SIZE");
> arch/x86/kernel/vmlinux.lds.S:370:. = ASSERT((_end - _text <= KERNEL_IMAGE_SIZE),
> arch/x86/kernel/vmlinux.lds.S:371:         "kernel image bigger than KERNEL_IMAGE_SIZE");
> 
> So what I'd do is keep KERNEL_IMAGE_SIZE and make it default 1G and use it
> everywhere.
> 
> Then, define a separate define which is used only in vmlinux.lds.S to
> enforce the size check. Having MAPPING_SIZE and IMAGE_SIZE is just
> needlessly confusing.

That sounds like the right solution to me - having two values is asking for 
trouble.

Thanks,

	Ingo