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

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Date:   Fri, 3 Mar 2017 16:23:19 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Baoquan He <bhe@...hat.com>
Cc:     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

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.

Especially if this is just some inconsistency you're addressing and not
some real issue.

BUT(!), don't take my word for it. Rather, do what the maintainers
propose. Who knows, they might have a much better idea.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--