linux-kernel - Re: [PATCH 1/4] x86/boot/compressed/64: Compile pagetable.c unconditionally

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Message-ID: <20171110091236.7o2vvmrty7eahziu@gmail.com>
Date:   Fri, 10 Nov 2017 10:12:36 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] x86/boot/compressed/64: Compile pagetable.c
 unconditionally


* Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:

> We are going to put few helpers into pagetable.c that are not specific
> to KASLR.
> 
> Let's make compilation of the file independent of KASLR and wrap
> KASLR-depended code into ifdef.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/boot/compressed/Makefile    | 2 +-
>  arch/x86/boot/compressed/pagetable.c | 5 +++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 65a150a7f15c..f7b64ecd09b3 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -77,7 +77,7 @@ vmlinux-objs-y := $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \
>  vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o
>  vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
>  ifdef CONFIG_X86_64
> -	vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/pagetable.o
> +	vmlinux-objs-y += $(obj)/pagetable.o
>  endif
>  
>  $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
> diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
> index f1aa43854bed..a15bbfcb3413 100644
> --- a/arch/x86/boot/compressed/pagetable.c
> +++ b/arch/x86/boot/compressed/pagetable.c
> @@ -27,6 +27,9 @@
>  /* These actually do the work of building the kernel identity maps. */
>  #include <asm/init.h>
>  #include <asm/pgtable.h>
> +
> +#ifdef CONFIG_RANDOMIZE_BASE
> +
>  /* Use the static base for this part of the boot process */
>  #undef __PAGE_OFFSET
>  #define __PAGE_OFFSET __PAGE_OFFSET_BASE
> @@ -149,3 +152,5 @@ void finalize_identity_maps(void)
>  {
>  	write_cr3(top_level_pgt);
>  }
> +
> +#endif /* CONFIG_RANDOMIZE_BASE */

The #ifdeffery becomes really ugly in this file. I think we should split these 
into separate .c files:

  arch/x86/boot/compressed/kaslr.c
  arch/x86/boot/compressed/5-level-paging.c

With core data structures and code and a well defined interface:

  arch/x86/boot/compressed/pagetable.c
  arch/x86/boot/compressed/pagetable.h

or so.

Thanks,

	Ingo