x86/PCI: X86_PAT & mprotect

Some versions of X used the mprotect workaround to change caching type from UC
to WB, so that it can then use mtrr to program WC for that region [1].  Change
the mmap of pci space through /sys or /proc interfaces from UC to UC_MINUS.
With this change, X will not need to use mprotect workaround to get WC type
since the MTRR mapping type will be honored.

The bug in mprotect that clobbers PAT bits is fixed in a follow on patch. So,
this X workaround will stop working as well.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 1 insertions, 3 deletions

diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 8af0f0bae2af..10fb308fded8 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -301,15 +301,13 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
         prot = pgprot_val(vma->vm_page_prot);
         if (pat_wc_enabled && write_combine)
                 prot |= _PAGE_CACHE_WC;
-        else if (pat_wc_enabled)
+        else if (pat_wc_enabled || boot_cpu_data.x86 > 3)
                 /*
                  * ioremap() and ioremap_nocache() defaults to UC MINUS for now.
                  * To avoid attribute conflicts, request UC MINUS here
                  * aswell.
                  */
                 prot |= _PAGE_CACHE_UC_MINUS;
-        else if (boot_cpu_data.x86 > 3)
-                prot |= _PAGE_CACHE_UC;
 
         vma->vm_page_prot = __pgprot(prot);