Re: [PATCH, v2] x86: use the right protections for split-up pagetables

Ingo Molnar
2009-02-20T08:03:29Z

* Ingo Molnar <mingo@elte.hu> wrote:

> [ Huang Ying also experienced problems in this area when writing
> the EFI code, but the real bug in split_large_page() was not
> realized back then. ]

> - * On Intel the NX bit of all levels must be cleared to make a
> - * page executable. See section 4.13.2 of Intel 64 and IA-32
> - * Architectures Software Developer's Manual).

Hm, in hindsight, we should have noticed this bug sooner - when
the NX comment above was added. There's never any good reason to
play protection games with higher-level pagetable entries. We
dont do it to user-space pagetables either - we just populate
them to _PAGE_TABLE and that's it.

Ingo