u‐boot mmu - MarekBykowski/readme GitHub Wiki

How it works

Set breakpoint, then run to it

hbreak -p cache_v8.c:setup_all_pgtables
cont

Print translation table at EL2N pointed to from TTBR0_EL2

mmu list tables
mmu print EL2N_S1_TTBR0_EL2

mmu list memory-maps
mmu memory-map EL2N_S1

Should be invalid as the translation tables haven't been set yet.

Read the page table address from u-boot printout, set a watchpoint there and print the memory afterwards

watch *0xfeff0000
x /4g 0xfeff0000

Upon filling in the translation tables x /4g 0xfeff0000 should return

EL2N:0x00000000FEFF0000:  0x0060000000000401	0x0060000040000401	0x0000000080000711	0x00000000C0000711

0x0060000000000401 is a block descriptor. Let us decipher it. Bits [54], [53], [10], [0] are set. OA (Output Address) noted below is on bits [47:42]. These are 0 so that VA 0 translates to PA 0 with the attributes XN=1, AF=1, SH=0x0, AP=0x0, Indx=0x0. What we have got left is to read the MAIR_EL2 to which the Indx=0x0 points to.

print /x $MAIR_EL2

MAIR_EL2 should be 0xFF440C0400 and our Indx=00 points to the first 8-bit chunk which is 0b0000000. All the zeros is Device memory

Print translation table at EL2N pointed to from TTBR0_EL2

mmu print EL2N_S1_TTBR0_EL2
mmu memory-map EL2N_S1

Use u-boot's API

U-boot defines a static mapping of the translation tables with the desired mapping and attributes. See here board/armltd/vexpress64/vexpress64.c

static struct mm_region vexpress64_mem_map[] = {                                
        {                                                                       
                .virt = V2M_PA_BASE,                                            
                .phys = V2M_PA_BASE,                                            
                .size = SZ_2G,                                                  
                .attrs = PTE_BLOCK_MEMTYPE(MT_DEVICE_NGNRNE) |                  
                         PTE_BLOCK_NON_SHARE |                                  
                         PTE_BLOCK_PXN | PTE_BLOCK_UXN                          
        }, {                                                                    
                .virt = V2M_DRAM_BASE,                                          
                .phys = V2M_DRAM_BASE,                                          
                .size = SZ_2G,                                                  
                .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) |                         
                         PTE_BLOCK_INNER_SHARE                                  
        }, {                                                                    
                /*                                                              
                 * DRAM beyond 2 GiB is located high. Let's map just some       
                 * of it, although U-Boot won't realistically use it, and       
                 * the actual available amount might be smaller on the model.   
                 */                                                             
                .virt = 0x880000000UL,          /* 32 + 2 GiB */                
                .phys = 0x880000000UL,                                          
                .size = 6UL * SZ_1G,                                            
                .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) |                         
                         PTE_BLOCK_INNER_SHARE                                  
        }, {                                                                    
                /* List terminator */                                           
                0,                                                              
        }                                                                       
};