1 2Virtual memory map with 4 level page tables: 3 40000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm 5hole caused by [47:63] sign extension 6ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor 7ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory 8ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole 9ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space 10ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole 11ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB) 12... unused hole ... 13ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB) 14... unused hole ... 15 vaddr_end for KASLR 16fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping 17fffffe8000000000 - fffffeffffffffff (=39 bits) LDT remap for PTI 18ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks 19... unused hole ... 20ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space 21... unused hole ... 22ffffffff80000000 - ffffffff9fffffff (=512 MB) kernel text mapping, from phys 0 23ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space 24[fixmap start] - ffffffffff5fffff kernel-internal fixmap range 25ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI 26ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole 27 28Virtual memory map with 5 level page tables: 29 300000000000000000 - 00ffffffffffffff (=56 bits) user space, different per mm 31hole caused by [56:63] sign extension 32ff00000000000000 - ff0fffffffffffff (=52 bits) guard hole, reserved for hypervisor 33ff10000000000000 - ff8fffffffffffff (=55 bits) direct mapping of all phys. memory 34ff90000000000000 - ff9fffffffffffff (=52 bits) LDT remap for PTI 35ffa0000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space (12800 TB) 36ffd2000000000000 - ffd3ffffffffffff (=49 bits) hole 37ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB) 38... unused hole ... 39ffdf000000000000 - fffffc0000000000 (=53 bits) kasan shadow memory (8PB) 40... unused hole ... 41 vaddr_end for KASLR 42fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping 43... unused hole ... 44ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks 45... unused hole ... 46ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space 47... unused hole ... 48ffffffff80000000 - ffffffff9fffffff (=512 MB) kernel text mapping, from phys 0 49ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space 50[fixmap start] - ffffffffff5fffff kernel-internal fixmap range 51ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI 52ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole 53 54Architecture defines a 64-bit virtual address. Implementations can support 55less. Currently supported are 48- and 57-bit virtual addresses. Bits 63 56through to the most-significant implemented bit are sign extended. 57This causes hole between user space and kernel addresses if you interpret them 58as unsigned. 59 60The direct mapping covers all memory in the system up to the highest 61memory address (this means in some cases it can also include PCI memory 62holes). 63 64vmalloc space is lazily synchronized into the different PML4/PML5 pages of 65the processes using the page fault handler, with init_top_pgt as 66reference. 67 68We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual 69memory window (this size is arbitrary, it can be raised later if needed). 70The mappings are not part of any other kernel PGD and are only available 71during EFI runtime calls. 72 73Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all 74physical memory, vmalloc/ioremap space and virtual memory map are randomized. 75Their order is preserved but their base will be offset early at boot time. 76 77Be very careful vs. KASLR when changing anything here. The KASLR address 78range must not overlap with anything except the KASAN shadow area, which is 79correct as KASAN disables KASLR. 80
