x86, PAT: Changing memtype to WC ensuring no WB alias
commit3869c4aa18835c8c61b44bd0f3ace36e9d3b5bd0
authorvenkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.com>
Thu, 9 Apr 2009 21:26:50 +0000 (9 14:26 -0700)
committerIngo Molnar <mingo@elte.hu>
Fri, 10 Apr 2009 11:55:47 +0000 (10 13:55 +0200)
treec983ab8206233bd571ff10ce307826a2e4126cc1
parent9fa3ab390abfc8b49fc0dd7c845b0ad224ec429f
x86, PAT: Changing memtype to WC ensuring no WB alias

As per SDM, there should not be any aliasing of a WC with any cacheable
type across CPUs. That is if one CPU is changing the identity map
memtype to _WC, no other CPU at the time of this change should not have a
TLB for this page that carries a WB attribute. SDM suggests to make the
page not present. But for that we will have to handle any page faults
that can potentially happen due to these pages being not present.

Other way to deal with this without having any WB mapping is to change
the page first to UC and then to WC. This ensures that we meet the SDM
requirement of no cacheable alais to WC page. This also has same or
lower overhead than marking the page not present and making it present
later.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20090409212708.797481000@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
arch/x86/mm/pageattr.c