x86: cpa, check if we changed anything and tlb flushing is necessary

Flush tlbs only when there was a real change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 17 insertions, 1 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index d1c08308ecbb..79a9f1b42ddd 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -21,6 +21,7 @@ struct cpa_data {
         int             numpages;
         pgprot_t        mask_set;
         pgprot_t        mask_clr;
+        int             flushtlb;
 };
 
 static inline int
@@ -329,11 +330,19 @@ repeat:
                  * not the memory it points to
                  */
                 new_pte = pfn_pte(pte_pfn(old_pte), canon_pgprot(new_prot));
-                set_pte_atomic(kpte, new_pte);
+
+                /*
+                 * Do we really change anything ?
+                 */
+                if (pte_val(old_pte) != pte_val(new_pte)) {
+                        set_pte_atomic(kpte, new_pte);
+                        cpa->flushtlb = 1;
+                }
         } else {
                 err = split_large_page(kpte, address);
                 if (!err)
                         goto repeat;
+                cpa->flushtlb = 1;
         }
         return err;
 }
@@ -438,10 +447,17 @@ static int change_page_attr_set_clr(unsigned long addr, int numpages,
         cpa.numpages = numpages;
         cpa.mask_set = mask_set;
         cpa.mask_clr = mask_clr;
+        cpa.flushtlb = 0;
 
         ret = __change_page_attr_set_clr(&cpa);
 
         /*
+         * Check whether we really changed something:
+         */
+        if (!cpa.flushtlb)
+                return ret;
+
+        /*
          * No need to flush, when we did not set any of the caching
          * attributes:
          */