| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ================= |
| Memory Management |
| ================= |
| |
| Complete virtual memory map with 4-level page tables |
| ==================================================== |
| |
| .. note:: |
| |
| - Negative addresses such as "-23 TB" are absolute addresses in bytes, counted down |
| from the top of the 64-bit address space. It's easier to understand the layout |
| when seen both in absolute addresses and in distance-from-top notation. |
| |
| For example 0xffffe90000000000 == -23 TB, it's 23 TB lower than the top of the |
| 64-bit address space (ffffffffffffffff). |
| |
| Note that as we get closer to the top of the address space, the notation changes |
| from TB to GB and then MB/KB. |
| |
| - "16M TB" might look weird at first sight, but it's an easier way to visualize size |
| notation than "16 EB", which few will recognize at first sight as 16 exabytes. |
| It also shows it nicely how incredibly large 64-bit address space is. |
| |
| :: |
| |
| ======================================================================================================================== |
| Start addr | Offset | End addr | Size | VM area description |
| ======================================================================================================================== |
| | | | | |
| 0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | | | | |
| 0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical |
| | | | | virtual memory addresses up to the -128 TB |
| | | | | starting offset of kernel mappings. |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | |
| | Kernel-space virtual memory, shared between all processes: |
| ____________________________________________________________|___________________________________________________________ |
| | | | | |
| ffff800000000000 | -128 TB | ffff87ffffffffff | 8 TB | ... guard hole, also reserved for hypervisor |
| ffff880000000000 | -120 TB | ffff887fffffffff | 0.5 TB | LDT remap for PTI |
| ffff888000000000 | -119.5 TB | ffffc87fffffffff | 64 TB | direct mapping of all physical memory (page_offset_base) |
| ffffc88000000000 | -55.5 TB | ffffc8ffffffffff | 0.5 TB | ... unused hole |
| ffffc90000000000 | -55 TB | ffffe8ffffffffff | 32 TB | vmalloc/ioremap space (vmalloc_base) |
| ffffe90000000000 | -23 TB | ffffe9ffffffffff | 1 TB | ... unused hole |
| ffffea0000000000 | -22 TB | ffffeaffffffffff | 1 TB | virtual memory map (vmemmap_base) |
| ffffeb0000000000 | -21 TB | ffffebffffffffff | 1 TB | ... unused hole |
| ffffec0000000000 | -20 TB | fffffbffffffffff | 16 TB | KASAN shadow memory |
| __________________|____________|__________________|_________|____________________________________________________________ |
| | |
| | Identical layout to the 56-bit one from here on: |
| ____________________________________________________________|____________________________________________________________ |
| | | | | |
| fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole |
| | | | | vaddr_end for KASLR |
| fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping |
| fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | ... unused hole |
| ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks |
| ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole |
| ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space |
| ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole |
| ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0 |
| ffffffff80000000 |-2048 MB | | | |
| ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space |
| ffffffffff000000 | -16 MB | | | |
| FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset |
| ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI |
| ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole |
| __________________|____________|__________________|_________|___________________________________________________________ |
| |
| |
| Complete virtual memory map with 5-level page tables |
| ==================================================== |
| |
| .. note:: |
| |
| - With 56-bit addresses, user-space memory gets expanded by a factor of 512x, |
| from 0.125 PB to 64 PB. All kernel mappings shift down to the -64 PB starting |
| offset and many of the regions expand to support the much larger physical |
| memory supported. |
| |
| :: |
| |
| ======================================================================================================================== |
| Start addr | Offset | End addr | Size | VM area description |
| ======================================================================================================================== |
| | | | | |
| 0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | | | | |
| 0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, still almost 64 bits wide hole of non-canonical |
| | | | | virtual memory addresses up to the -64 PB |
| | | | | starting offset of kernel mappings. |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | |
| | Kernel-space virtual memory, shared between all processes: |
| ____________________________________________________________|___________________________________________________________ |
| | | | | |
| ff00000000000000 | -64 PB | ff0fffffffffffff | 4 PB | ... guard hole, also reserved for hypervisor |
| ff10000000000000 | -60 PB | ff10ffffffffffff | 0.25 PB | LDT remap for PTI |
| ff11000000000000 | -59.75 PB | ff90ffffffffffff | 32 PB | direct mapping of all physical memory (page_offset_base) |
| ff91000000000000 | -27.75 PB | ff9fffffffffffff | 3.75 PB | ... unused hole |
| ffa0000000000000 | -24 PB | ffd1ffffffffffff | 12.5 PB | vmalloc/ioremap space (vmalloc_base) |
| ffd2000000000000 | -11.5 PB | ffd3ffffffffffff | 0.5 PB | ... unused hole |
| ffd4000000000000 | -11 PB | ffd5ffffffffffff | 0.5 PB | virtual memory map (vmemmap_base) |
| ffd6000000000000 | -10.5 PB | ffdeffffffffffff | 2.25 PB | ... unused hole |
| ffdf000000000000 | -8.25 PB | fffffbffffffffff | ~8 PB | KASAN shadow memory |
| __________________|____________|__________________|_________|____________________________________________________________ |
| | |
| | Identical layout to the 47-bit one from here on: |
| ____________________________________________________________|____________________________________________________________ |
| | | | | |
| fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole |
| | | | | vaddr_end for KASLR |
| fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping |
| fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | ... unused hole |
| ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks |
| ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole |
| ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space |
| ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole |
| ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0 |
| ffffffff80000000 |-2048 MB | | | |
| ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space |
| ffffffffff000000 | -16 MB | | | |
| FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset |
| ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI |
| ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole |
| __________________|____________|__________________|_________|___________________________________________________________ |
| |
| Architecture defines a 64-bit virtual address. Implementations can support |
| less. Currently supported are 48- and 57-bit virtual addresses. Bits 63 |
| through to the most-significant implemented bit are sign extended. |
| This causes hole between user space and kernel addresses if you interpret them |
| as unsigned. |
| |
| The direct mapping covers all memory in the system up to the highest |
| memory address (this means in some cases it can also include PCI memory |
| holes). |
| |
| vmalloc space is lazily synchronized into the different PML4/PML5 pages of |
| the processes using the page fault handler, with init_top_pgt as |
| reference. |
| |
| We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual |
| memory window (this size is arbitrary, it can be raised later if needed). |
| The mappings are not part of any other kernel PGD and are only available |
| during EFI runtime calls. |
| |
| Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all |
| physical memory, vmalloc/ioremap space and virtual memory map are randomized. |
| Their order is preserved but their base will be offset early at boot time. |
| |
| Be very careful vs. KASLR when changing anything here. The KASLR address |
| range must not overlap with anything except the KASAN shadow area, which is |
| correct as KASAN disables KASLR. |
| |
| For both 4- and 5-level layouts, the STACKLEAK_POISON value in the last 2MB |
| hole: ffffffffffff4111 |
