kdump -- Linux Kernel 欣赏

/*
	先说 CONFIG_PGTABLE_LEVEL = 3 的情况吧.
	
	这个 映射层级 kernel 会自己计算的:
	 1: 
	 Page size (4KB)  --->   
	 Virtual address space size (39-bit)  --->
     Symbol: PGTABLE_LEVELS [=3]       
     Defined at arch/arm64/Kconfig:224     

	它就是获取 pmd表的项嘛, 就是 pte表的起始地址.
	其算法还是基地址 + 偏移量
	偏移量就是 pmd_index(), 下面说说 基地址 .                                                                                                                                                                                        		   
*/
static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
{
    
    
	return (pmd_t *)pud_page_vaddr(*pud) + pmd_index(address);
}

static inline unsigned long pmd_index(unsigned long address)
{
    
    
	return (address >> PMD_SHIFT) & (PTRS_PER_PMD - 1);
}