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Diffstat (limited to 'Documentation/x86/x86_64/mm.txt')
| -rw-r--r-- | Documentation/x86/x86_64/mm.txt | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt new file mode 100644 index 000000000..05ef53d83 --- /dev/null +++ b/Documentation/x86/x86_64/mm.txt @@ -0,0 +1,81 @@ + +Virtual memory map with 4 level page tables: + +0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm +hole caused by [47:63] sign extension +ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor +ffff880000000000 - ffff887fffffffff (=39 bits) LDT remap for PTI +ffff888000000000 - ffffc87fffffffff (=64 TB) direct mapping of all phys. memory +ffffc88000000000 - ffffc8ffffffffff (=39 bits) hole +ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space +ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole +ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB) +... unused hole ... +ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB) +... unused hole ... + vaddr_end for KASLR +fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping +fffffe8000000000 - fffffeffffffffff (=39 bits) LDT remap for PTI +ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks +... unused hole ... +ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space +... unused hole ... +ffffffff80000000 - ffffffff9fffffff (=512 MB) kernel text mapping, from phys 0 +ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space +[fixmap start] - ffffffffff5fffff kernel-internal fixmap range +ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI +ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole + +Virtual memory map with 5 level page tables: + +0000000000000000 - 00ffffffffffffff (=56 bits) user space, different per mm +hole caused by [56:63] sign extension +ff00000000000000 - ff0fffffffffffff (=52 bits) guard hole, reserved for hypervisor +ff10000000000000 - ff10ffffffffffff (=48 bits) LDT remap for PTI +ff11000000000000 - ff90ffffffffffff (=55 bits) direct mapping of all phys. memory +ff91000000000000 - ff9fffffffffffff (=3840 TB) hole +ffa0000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space (12800 TB) +ffd2000000000000 - ffd3ffffffffffff (=49 bits) hole +ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB) +... unused hole ... +ffdf000000000000 - fffffc0000000000 (=53 bits) kasan shadow memory (8PB) +... unused hole ... + vaddr_end for KASLR +fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping +... unused hole ... +ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks +... unused hole ... +ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space +... unused hole ... +ffffffff80000000 - ffffffff9fffffff (=512 MB) kernel text mapping, from phys 0 +ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space +[fixmap start] - ffffffffff5fffff kernel-internal fixmap range +ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI +ffffffffffe00000 - 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. |