x86 PAT: consolidate old memtype new memtype check into a function

Impact: cleanup

Move the new memtype old memtype allowed check to header so that is can be
shared by other users. Subsequent patch uses this in pat.c in remap_pfn_range()
code path. No functionality change in this patch.

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>

1 files changed, 19 insertions, 0 deletions

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 83e69f4a37f0..06bbcbd66e9c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -341,6 +341,25 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 
 #define canon_pgprot(p) __pgprot(pgprot_val(p) & __supported_pte_mask)
 
+static inline int is_new_memtype_allowed(unsigned long flags,
+                                                unsigned long new_flags)
+{
+        /*
+         * Certain new memtypes are not allowed with certain
+         * requested memtype:
+         * - request is uncached, return cannot be write-back
+         * - request is write-combine, return cannot be write-back
+         */
+        if ((flags == _PAGE_CACHE_UC_MINUS &&
+             new_flags == _PAGE_CACHE_WB) ||
+            (flags == _PAGE_CACHE_WC &&
+             new_flags == _PAGE_CACHE_WB)) {
+                return 0;
+        }
+
+        return 1;
+}
+
 #ifndef __ASSEMBLY__
 /* Indicate that x86 has its own track and untrack pfn vma functions */
 #define __HAVE_PFNMAP_TRACKING