svn commit: r281495 - in head/sys: conf i386/i386 i386/include x86/acpica

[Benjamin Kaduk]

On Mon, Apr 13, 2015 at 11:22 AM, Konstantin Belousov <kib at freebsd.org>
wrote:

> Author: kib
> Date: Mon Apr 13 15:22:45 2015
> New Revision: 281495
> URL: https://svnweb.freebsd.org/changeset/base/281495
>
> Log:
>   Add config option PAE_TABLES for the i386 kernel.  It switches pmap to
>   use PAE format for the page tables, but does not incur other
>   consequences of the full PAE config.  In particular, vm_paddr_t and
>   bus_addr_t are left 32bit, and max supported memory is still limited
>   by 4GB.
>
>   The option allows to have nx permissions for memory mappings on i386
>   kernel, while keeping the usual i386 KBI and avoiding the kernel data
>   sizing problems typical for the PAE config.
>
>   Intel documented that the PAE format for page tables is available
>   starting with the Pentium Pro, but it is possible that the plain
>   Pentium CPUs have the required support (Appendix H).  The goal is to
>   enable the option and non-exec mappings on i386 for the GENERIC
>   kernel.  Anybody wanting a useful system on 486, have to reconfigure
>   the modern i386 kernel anyway.
>
>   Discussed with:       alc, jhb
>   Sponsored by: The FreeBSD Foundation
>   MFC after:    2 weeks
>

relnotes: yes?

-Ben