Walleij: New ARM32 Security Features in v6.10

Linus Walleij writesabout a pair of security features for 32-bit Arm systems; these landedin 6.10, but, he says, have now stabilized to the point that distributorsmay want to enable them.

PAN is an abbreviation for the somewhat grammatically incorrectPrivileged Access Never. [...]

For modern ARM32 systems with large memories configured to use LPAEnothing like PAN was available: this version of the MMU simply didnot implement a PAN option.

As of the patch originally developed by Catalin Marinas, we deploya scheme that will use the fact that LPAE has two separatetranslation table base registers (TTBR:s): one for userspace(TTBR0) and one for kernelspace (TTBR1).