linux-kernel - Re: [PATCH v5 12/13] x86, 64bit: Print init kernel lowmap correctly

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Date:	Fri, 21 Dec 2012 17:26:19 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 12/13] x86, 64bit: Print init kernel lowmap correctly

> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 4178530..30f6190 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -304,10 +304,14 @@ 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 + (max_pfn_mapped << PAGE_SHIFT);
> +	unsigned long vaddr_end = __START_KERNEL_map + KERNEL_IMAGE_SIZE;

Should you remove the line in head64.c that sets the
max_pfn_mapped to KERNEL_IMAGE_SIZE >> PAGE_SHIFT?

>  	unsigned long end = roundup((unsigned long)_brk_end, PMD_SIZE) - 1;
>  	pmd_t *pmd = level2_kernel_pgt;
>  
> +	/* Xen has its own end somehow with abused max_pfn_mapped */

Could you clarify please?

My recollection is that the max_pfn_mapped would point to the end of the
RAMdisk. And yes (from mmu.c):

   1862         /* max_pfn_mapped is the last pfn mapped in the initial memory
   1863          * mappings. Considering that on Xen after the kernel mappings we
   1864          * have the mappings of some pages that don't exist in pfn space, we
   1865          * set max_pfn_mapped to the last real pfn mapped. */
   1866         max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->mfn_list));
   1867 

And if you follow xen_start_info, you get to include/xen/interface/xen.h which has:

    406  *  4. This the order of bootstrap elements in the initial virtual region:
    407  *      a. relocated kernel image
    408  *      b. initial ram disk              [mod_start, mod_len]
    409  *      c. list of allocated page frames [mfn_list, nr_pages]

so per that code I believe max_pfn_mapped covers the kernel and the ramdisk - no more.


> +	if (max_pfn_mapped)
> +		vaddr_end = __START_KERNEL_map + (max_pfn_mapped << PAGE_SHIFT);
> +
>  	for (; vaddr + PMD_SIZE - 1 < vaddr_end; pmd++, vaddr += PMD_SIZE) {
>  		if (pmd_none(*pmd))
>  			continue;
> -- 

This part of the patch does not seem to have much to do with the printk?
Should it be seperate patch?
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