[PATCH 1/1] UBUNTU: Disable 4MB page tables for Atom, work around errata AAE44

[Tim Gardner]

Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/523112
> 
> This patch addresses Intel errata AAE44 by totally disabling 4MB
> pages and thus avoiding avoiding large pages being split into
> smaller 4K pages and thus never tripping this CPU feature.
> 
> The bug can manifests itself as instruction fetch oopses on seemingly
> legitimate executable pages.
> 
> Errata AAE44 (http://download.intel.com/design/processor/specupdt/319536.pdf
> page 33) states:
> 
> "If software clears the PS (page size) bit in a present PDE (page directory
> entry), that will cause linear addresses mapped through this PDE to use
> 4-KByte pages instead of using a large page after old TLB entries are
> invalidated. Due to this erratum, if a code fetch uses this PDE before the
> TLB entry for the large page is invalidated then it may fetch from a different
> physical address than specified by either the old large page translation or
> the new 4-KByte page translation. This erratum may also cause speculative code
> fetches from incorrect addresses."
> 
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---
>  arch/x86/kernel/cpu/bugs.c |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 

Methinks you should send this to Ingo and hpa as I believe its worthy of
a stable update as well as upstream inclusion.

rtg
-- 
Tim Gardner tim.gardner at canonical.com