linux-kernel - Re: [PATCH v2 1/3] x86/KASLR: Update document about KERNEL_IMAGE

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Message-ID: <20181003084337.GA5140@MiWiFi-R3L-srv>
Date:   Wed, 3 Oct 2018 16:43:37 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-doc@...r.kernel.org, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com, thgarnie@...gle.com,
        corbet@....net
Subject: Re: [PATCH v2 1/3] x86/KASLR: Update document about KERNEL_IMAGE_SIZE

On 10/03/18 at 09:52am, Ingo Molnar wrote:
> 
> * Baoquan He <bhe@...hat.com> wrote:
> 
> > Currently CONFIG_RANDOMIZE_BASE=y is default set, update the relevant
> > document about KERNEL_IMAGE_SIZE.
> 
> Suggested wording:
> 
>   x86/KASLR: Update KERNEL_IMAGE_SIZE description
>   
>   Currently CONFIG_RANDOMIZE_BASE=y is set by default, which makes some of the
>   old comments above the KERNEL_IMAGE_SIZE definition out of date. Update them
>   to the current state of affairs.

Thanks, will update with this.

> 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  arch/x86/include/asm/page_64_types.h | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> > index 6afac386a434..2288ceabdb9c 100644
> > --- a/arch/x86/include/asm/page_64_types.h
> > +++ b/arch/x86/include/asm/page_64_types.h
> > @@ -61,9 +61,10 @@
> >  /*
> >   * Kernel image size is limited to 1GiB due to the fixmap living in the
> >   * next 1GiB (see level2_kernel_pgt in arch/x86/kernel/head_64.S). Use
> > - * 512MiB by default, leaving 1.5GiB for modules once the page tables
> > - * are fully set up. If kernel ASLR is configured, it can extend the
> > - * kernel page table mapping, reducing the size of the modules area.
> > + * 1 GiB by default, leaving 1 GiB for modules once the page tables are
> > + * fully set up. If kernel ASLR is not configured, it can shrink the
> > + * kernel page table mapping to decrease the size of kernel area to 512
> > + * MiB, increase the size of the modules area to 1.5 GiB.
> >   */
> 
> I've prettified that comment some more:

Thanks, will use them.

> 
>  /*
>   * Maximum kernel image size is limited to 1 GiB, due to the fixmap living
>   * in the next 1 GiB (see level2_kernel_pgt in arch/x86/kernel/head_64.S).
>   *
>   * On KASLR use 1 GiB by default, leaving 1 GiB for modules once the
>   * page tables are fully set up.
>   *
>   * If KASLR is disabled we can shrink it to 0.5 GiB and increase the size
>   * of the modules area to 1.5 GiB.
>   */
> 
> >  #if defined(CONFIG_RANDOMIZE_BASE)
> >  #define KERNEL_IMAGE_SIZE	(1024 * 1024 * 1024)
> 
> BTW., while at it, shouldn't we make that:
> 
>    #ifdef CONFIG_RANDOMIZE_BASE

Yes, makes sense, will change.

> 
> ?
> 
> Thanks,
> 
> 	Ingo