Re: [PATCH 07/19] x86, mm: Remove early_memremap workaround for page table accessing on 64bit

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

On Thu, Oct 18, 2012 at 01:50:18PM -0700, Yinghai Lu wrote:
> We do not need that workaround anymore after patches that pre-map page
> table buf and do not clear initial page table wrongly.


.. and somewhere during the v2 posting we had a discussion about
why this work-around came about. You should include a bit about
that and copy-n-paste some of that here please.


> 
> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> ---
>  arch/x86/mm/init_64.c |   38 ++++----------------------------------
>  1 files changed, 4 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7dfa69b..4e6873f 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -340,36 +340,12 @@ static __ref void *alloc_low_page(unsigned long *phys)
>  	} else
>  		pfn = pgt_buf_end++;
>  
> -	adr = early_memremap(pfn * PAGE_SIZE, PAGE_SIZE);
> +	adr = __va(pfn * PAGE_SIZE);
>  	clear_page(adr);
>  	*phys  = pfn * PAGE_SIZE;
>  	return adr;
>  }
>  
> -static __ref void *map_low_page(void *virt)
> -{
> -	void *adr;
> -	unsigned long phys, left;
> -
> -	if (after_bootmem)
> -		return virt;
> -
> -	phys = __pa(virt);
> -	left = phys & (PAGE_SIZE - 1);
> -	adr = early_memremap(phys & PAGE_MASK, PAGE_SIZE);
> -	adr = (void *)(((unsigned long)adr) | left);
> -
> -	return adr;
> -}
> -
> -static __ref void unmap_low_page(void *adr)
> -{
> -	if (after_bootmem)
> -		return;
> -
> -	early_iounmap((void *)((unsigned long)adr & PAGE_MASK), PAGE_SIZE);
> -}
> -
>  static unsigned long __meminit
>  phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end,
>  	      pgprot_t prot)
> @@ -441,10 +417,9 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,
>  		if (pmd_val(*pmd)) {
>  			if (!pmd_large(*pmd)) {
>  				spin_lock(&init_mm.page_table_lock);
> -				pte = map_low_page((pte_t *)pmd_page_vaddr(*pmd));
> +				pte = (pte_t *)pmd_page_vaddr(*pmd);
>  				last_map_addr = phys_pte_init(pte, address,
>  								end, prot);
> -				unmap_low_page(pte);
>  				spin_unlock(&init_mm.page_table_lock);
>  				continue;
>  			}
> @@ -480,7 +455,6 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,
>  
>  		pte = alloc_low_page(&pte_phys);
>  		last_map_addr = phys_pte_init(pte, address, end, new_prot);
> -		unmap_low_page(pte);
>  
>  		spin_lock(&init_mm.page_table_lock);
>  		pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
> @@ -515,10 +489,9 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
>  
>  		if (pud_val(*pud)) {
>  			if (!pud_large(*pud)) {
> -				pmd = map_low_page(pmd_offset(pud, 0));
> +				pmd = pmd_offset(pud, 0);
>  				last_map_addr = phys_pmd_init(pmd, addr, end,
>  							 page_size_mask, prot);
> -				unmap_low_page(pmd);
>  				__flush_tlb_all();
>  				continue;
>  			}
> @@ -555,7 +528,6 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
>  		pmd = alloc_low_page(&pmd_phys);
>  		last_map_addr = phys_pmd_init(pmd, addr, end, page_size_mask,
>  					      prot);
> -		unmap_low_page(pmd);
>  
>  		spin_lock(&init_mm.page_table_lock);
>  		pud_populate(&init_mm, pud, __va(pmd_phys));
> @@ -591,17 +563,15 @@ kernel_physical_mapping_init(unsigned long start,
>  			next = end;
>  
>  		if (pgd_val(*pgd)) {
> -			pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
> +			pud = (pud_t *)pgd_page_vaddr(*pgd);
>  			last_map_addr = phys_pud_init(pud, __pa(start),
>  						 __pa(end), page_size_mask);
> -			unmap_low_page(pud);
>  			continue;
>  		}
>  
>  		pud = alloc_low_page(&pud_phys);
>  		last_map_addr = phys_pud_init(pud, __pa(start), __pa(next),
>  						 page_size_mask);
> -		unmap_low_page(pud);
>  
>  		spin_lock(&init_mm.page_table_lock);
>  		pgd_populate(&init_mm, pgd, __va(pud_phys));
> -- 
> 1.7.7
> 
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