From 3869c4aa18835c8c61b44bd0f3ace36e9d3b5bd0 Mon Sep 17 00:00:00 2001 From: "venkatesh.pallipadi@intel.com" Date: Thu, 9 Apr 2009 14:26:50 -0700 Subject: 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 Signed-off-by: Suresh Siddha LKML-Reference: <20090409212708.797481000@intel.com> Signed-off-by: Ingo Molnar diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 985eef8..797f9f1 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -1000,8 +1000,15 @@ EXPORT_SYMBOL(set_memory_array_uc); int _set_memory_wc(unsigned long addr, int numpages) { - return change_page_attr_set(&addr, numpages, + int ret; + ret = change_page_attr_set(&addr, numpages, + __pgprot(_PAGE_CACHE_UC_MINUS), 0); + + if (!ret) { + ret = change_page_attr_set(&addr, numpages, __pgprot(_PAGE_CACHE_WC), 0); + } + return ret; } int set_memory_wc(unsigned long addr, int numpages) -- cgit v0.10.2