Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file

[Catalin Marinas]

On Tue, Jul 16, 2019 at 11:31:27AM +0800, Guo Ren wrote:
> I saw arm64 to prevent speculation by temporarily setting TTBR0.el1 to
> a zero page table. Is that used to prevent speculative execution user
> space code or just prevent ld/st in copy_use_* ?

Only to prevent explicit ld/st from user. On ARMv8.1+, we don't normally
use the TTBR0 trick but rather disable user space access using the PAN
(privileged access never) feature. However, I don't think PAN disables
speculative accesses, only explicit loads/stores. Also, with ARMv8.2
Linux uses the LDTR/STTR instructions in copy_*_user() which don't need
to disable PAN explicitly.

-- 
Catalin