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 <[email protected]>
Signed-off-by: Suresh Siddha <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Jesse Barnes <[email protected]>

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);