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

From: Konrad Rzeszutek Wilk
Date: Fri Dec 21 2012 - 17:26:30 EST


> 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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