linux-kernel - Re: [PATCH 1/2] x86/64: Make kernel text mapping always take one whole page table in early boot code

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Date:   Thu, 8 Dec 2016 14:24:32 +0600
From:   Alexnader Kuleshov <kuleshovmail@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, hpa@...or.com,
        mingo@...hat.com, x86@...nel.org, keescook@...omium.org,
        yinghai@...nel.org, bp@...e.de, thgarnie@...gle.com,
        kuleshovmail@...il.com, luto@...nel.org, anderson@...hat.com,
        dyoung@...hat.com, xlpang@...hat.com
Subject: Re: [PATCH 1/2] x86/64: Make kernel text mapping always take one
 whole page table in early boot code

On 12-08-16, Baoquan He wrote:
> In early boot code level2_kernel_pgt is used to map kernel text. And its
> size varies according to KERNEL_IMAGE_SIZE and fixed at compiling time.
> In fact we can make it always takes 512 entries of one whople page table,
> because later function cleanup_highmap will clean up the unused entries.
> With the help of this change kernel text mapping size can be decided at
> runtime later, 512M if kaslr is disabled, 1G if kaslr is enabled.

s/whople/whole

> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  arch/x86/include/asm/page_64_types.h |  3 ++-
>  arch/x86/kernel/head_64.S            | 15 ++++++++-------
>  arch/x86/mm/init_64.c                |  2 +-
>  3 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 9215e05..62a20ea 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -56,8 +56,9 @@
>   * are fully set up. If kernel ASLR is configured, it can extend the
>   * kernel page table mapping, reducing the size of the modules area.
>   */
> +#define KERNEL_MAPPING_SIZE_EXT	(1024 * 1024 * 1024)
>  #if defined(CONFIG_RANDOMIZE_BASE)
> -#define KERNEL_IMAGE_SIZE	(1024 * 1024 * 1024)
> +#define KERNEL_IMAGE_SIZE	KERNEL_MAPPING_SIZE_EXT
>  #else
>  #define KERNEL_IMAGE_SIZE	(512 * 1024 * 1024)
>  #endif
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index b4421cc..c4b40e7c9 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -453,17 +453,18 @@ NEXT_PAGE(level3_kernel_pgt)
>  
>  NEXT_PAGE(level2_kernel_pgt)
>  	/*
> -	 * 512 MB kernel mapping. We spend a full page on this pagetable
> -	 * anyway.
> +	 * Kernel image size is limited to 512 MB. The kernel code+data+bss
> +	 * must not be bigger than that.
>  	 *
> -	 * The kernel code+data+bss must not be bigger than that.
> +	 * We spend a full page on this pagetable anyway, so take the whole
> +	 * page here so that the kernel mapping size can be decided at runtime,
> +	 * 512M if no kaslr, 1G if kaslr enabled. Later cleanup_highmap will
> +	 * clean up those unused entries.
>  	 *
> -	 * (NOTE: at +512MB starts the module area, see MODULES_VADDR.
> -	 *  If you want to increase this then increase MODULES_VADDR
> -	 *  too.)
> +	 * The module area starts after kernel mapping area.
>  	 */
>  	PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
> -		KERNEL_IMAGE_SIZE/PMD_SIZE)
> +		PTRS_PER_PMD)
>  
>  NEXT_PAGE(level2_fixmap_pgt)
>  	.fill	506,8,0
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 14b9dd7..e95b977 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -307,7 +307,7 @@ void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
>  void __init cleanup_highmap(void)
>  {
>  	unsigned long vaddr = __START_KERNEL_map;
> -	unsigned long vaddr_end = __START_KERNEL_map + KERNEL_IMAGE_SIZE;
> +	unsigned long vaddr_end = __START_KERNEL_map + KERNEL_MAPPING_SIZE_EXT;
>  	unsigned long end = roundup((unsigned long)_brk_end, PMD_SIZE) - 1;
>  	pmd_t *pmd = level2_kernel_pgt;
>  
> -- 
> 2.5.5
>