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Virtual memory map with 4 level page tables:
0000000000000000 - 00007fffffffffff (=47 bits, 128 TB) user space, different per mm
hole caused by [47:63] sign extension
ffff800000000000 - ffff87ffffffffff (=43 bits, 8 TB) guard hole, reserved for hypervisor
ffff880000000000 - ffffc7ffffffffff (=46 bits, 64 TB) direct mapping of all phys. memory (page_offset_base)
ffffc80000000000 - ffffc8ffffffffff (=40 bits, 1 TB) unused hole
ffffc90000000000 - ffffe8ffffffffff (=45 bits, 32 TB) vmalloc/ioremap space (vmalloc_base)
ffffe90000000000 - ffffe9ffffffffff (=40 bits, 1 TB) unused hole
ffffea0000000000 - ffffeaffffffffff (=40 bits, 1 TB) virtual memory map (vmemmap_base)
ffffeb0000000000 - ffffebffffffffff (=40 bits, 1 TB) unused hole
ffffec0000000000 - fffffbffffffffff (=44 bits, 16 TB) kasan shadow memory
fffffc0000000000 - fffffdffffffffff (=41 bits, 2 TB) unused hole
vaddr_end for KASLR
fffffe0000000000 - fffffe7fffffffff (=39 bits, 512 GB) cpu_entry_area mapping
fffffe8000000000 - fffffeffffffffff (=39 bits, 512 GB) LDT remap for PTI
ffffff0000000000 - ffffff7fffffffff (=39 bits, 512 GB) %esp fixup stacks
ffffff8000000000 - fffffffeefffffff (~39 bits, ~507 GB) unused hole
ffffffef00000000 - fffffffeffffffff (=36 bits, 64 GB) EFI region mapping space
ffffffff00000000 - ffffffff7fffffff (=31 bits, 2 GB) unused hole
ffffffff80000000 - ffffffff9fffffff (=29 bits, 512 MB) kernel text mapping, from phys 0
ffffffffa0000000 - fffffffffeffffff (~31 bits, 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, 64 PB) user space, different per mm
hole caused by [56:63] sign extension
ff00000000000000 - ff0fffffffffffff (=52 bits, 4 PB) guard hole, reserved for hypervisor
ff10000000000000 - ff8fffffffffffff (=55 bits, 32 PB) direct mapping of all phys. memory (page_offset_base)
ff90000000000000 - ff9fffffffffffff (=52 bits, 4 PB) LDT remap for PTI
ffa0000000000000 - ffd1ffffffffffff (=53 bits, 12800 TB) vmalloc/ioremap space (vmalloc_base)
ffd2000000000000 - ffd3ffffffffffff (=49 bits, 512 TB) unused hole
ffd4000000000000 - ffd5ffffffffffff (=49 bits, 512 TB) virtual memory map (vmemmap_base)
ffd6000000000000 - ffdeffffffffffff (~51 bits, 2304 TB) unused hole
ffdf000000000000 - fffffdffffffffff (~53 bits, ~8 PB) kasan shadow memory
fffffc0000000000 - fffffdffffffffff (=41 bits, 2 TB) unused hole
vaddr_end for KASLR
fffffe0000000000 - fffffe7fffffffff (=39 bits, 512 GB) cpu_entry_area mapping
fffffe8000000000 - fffffeffffffffff (=39 bits, 512 GB) unused hole
ffffff0000000000 - ffffff7fffffffff (=39 bits, 512 GB) %esp fixup stacks
ffffff8000000000 - ffffffeeffffffff (~39 bits, 444 GB) unused hole
ffffffef00000000 - fffffffeffffffff (=36 bits, 64 GB) EFI region mapping space
ffffffff00000000 - ffffffff7fffffff (31 bits, 2 GB) unused hole
ffffffff80000000 - ffffffff9fffffff (=29 bits, 512 MB) kernel text mapping, from phys 0
ffffffffa0000000 - fffffffffeffffff (~31 bits, 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.
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