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Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING_SIZE

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING_SIZE
Date	2017-03-16 09:20 +0100
Message-ID	<tlyNz-3TH-1@gated-at.bofh.it> (permalink)
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* Borislav Petkov <bp@suse.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

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Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING_SIZE Ingo Molnar <mingo@kernel.org> - 2017-03-16 09:20 +0100
  Re: [PATCH v4 1/3] x86: Introduce a new constant KERNEL_MAPPING_SIZE Baoquan He <bhe@redhat.com> - 2017-03-16 10:50 +0100

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