theory: fix userspace bits

related issue: #695

Thank you @m4p1e

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
pull/818/head
Alexander Kuleshov 2 years ago
parent ff10a7b0f1
commit 4d6cf71f67

@ -171,7 +171,7 @@ This solution is `sign extension`. Here we can see that the lower 48 bits of a v
* Kernel space
* Userspace
Userspace occupies the lower part of the virtual address space, from `0x000000000000000` to `0x00007fffffffffff` and kernel space occupies the highest part from `0xffff8000000000` to `0xffffffffffffffff`. Note that bits `63:48` is 0 for userspace and 1 for kernel space. All addresses which are in kernel space and in userspace or in other words which higher `63:48` bits are zeroes or ones are called `canonical` addresses. There is a `non-canonical` area between these memory regions. Together these two memory regions (kernel space and user space) are exactly `2^48` bits wide. We can find the virtual memory map with 4 level page tables in the [Documentation/x86/x86_64/mm.txt](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/Documentation/x86/x86_64/mm.txt):
Userspace occupies the lower part of the virtual address space, from `0x000000000000000` to `0x00007fffffffffff` and kernel space occupies the highest part from `0xffff8000000000` to `0xffffffffffffffff`. Note that bits `63:47` is 0 for userspace and 1 for kernel space. All addresses which are in kernel space and in userspace or in other words which higher `63:48` bits are zeroes or ones are called `canonical` addresses. There is a `non-canonical` area between these memory regions. Together these two memory regions (kernel space and user space) are exactly `2^48` bits wide. We can find the virtual memory map with 4 level page tables in the [Documentation/x86/x86_64/mm.txt](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/Documentation/x86/x86_64/mm.txt):
```
0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm

Loading…
Cancel
Save