The same problem I asked before. I want to modify kernel image's page table from 2M to 4K. In arch/x86/kernel/head_64.S, I add another level page table, make pmd point to the new page table. However, after compile and boot it, the kernel cannot work and always reboot. I try many kind of port, it still cannot work normally. Here is the context of my modified code : ----------------------------------------------------- /* Automate the creation of 1 to 1 mapping pmd entries */ #define PMDS(START, PERM, COUNT) \ i = 0 ; \ .rept (COUNT) ; \ .quad (START) + (i << PMD_SHIFT) + (PERM) ; \ i = i + 1 ; \ .endr #define PTDS(START, PERM, COUNT) \ i = 0 ; \ .rept (COUNT) ; \ .quad (START) + (i << PAGE_SHIFT) + (PERM) ; \ i = i + 1 ; \ .endr .data /* * This default setting generates an ident mapping at address 0x100000 * and a mapping for the kernel that precisely maps virtual address * 0xffffffff80000000 to physical address 0x000000. (always using * 2Mbyte large pages provided by PAE mode) */ NEXT_PAGE(init_level4_pgt) .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE .org init_level4_pgt + L4_PAGE_OFFSET*8, 0 .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE .org init_level4_pgt + L4_START_KERNEL*8, 0 /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */ .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE NEXT_PAGE(level3_ident_pgt) .quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE .fill 511,8,0 NEXT_PAGE(level3_kernel_pgt) .fill L3_START_KERNEL,8,0 /* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */ .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE .quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE NEXT_PAGE(level2_fixmap_pgt) .fill 506,8,0 .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE /* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */ .fill 5,8,0 NEXT_PAGE(level1_fixmap_pgt) .fill 512,8,0 NEXT_PAGE(level2_ident_pgt) /* Since I easily can, map the first 1G. * Don't set NX because code runs from these pages. */ PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD) NEXT_PAGE(level2_kernel_pgt) /* * 512 MB kernel mapping. We spend a full page on this pagetable * anyway. * * The kernel code+data+bss must not be bigger than that. * * (NOTE: at +512MB starts the module area, see MODULES_VADDR. * If you want to increase this then increase MODULES_VADDR * too.) */ /* PMDS(0, __PAGE_KERNEL_LARGE_EXEC, KERNEL_IMAGE_SIZE/PMD_SIZE)*/ #define NEW_PMD_PORT (0x0 | _PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED) PMDS(level1_kernel_pgt - __START_KERNEL_map, NEW_PMD_PORT, PTRS_PER_PMD) NEXT_PAGE(level1_kernel_pgt) #define NEW_PTD_PORT (0x0 | _PAGE_PRESENT | _PAGE_RW | |_PAGE_USER | _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_GLOBAL) PTDS(0, NEW_PTD_PORT, KERNEL_IMAGE_SIZE/PAGE_SIZE) NEXT_PAGE(level2_spare_pgt) .fill 512, 8, 0 ----------------------------------------------------------------------------------------------