KVM: s390/mm: new gmap_test_and_clear_dirty function

For live migration kvm needs to test and clear the dirty bit of guest pages.

That for is ptep_test_and_clear_user_dirty, to be sure we are not racing with
other code, we protect the pte. This needs to be done within
the architecture memory management code.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

2 files changed, 23 insertions, 0 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index b2c630df0ca5..fcba5e03839f 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -838,6 +838,8 @@ unsigned long __gmap_fault(unsigned long address, struct gmap *);
 unsigned long gmap_fault(unsigned long address, struct gmap *);
 void gmap_discard(unsigned long from, unsigned long to, struct gmap *);
 void __gmap_zap(unsigned long address, struct gmap *);
+bool gmap_test_and_clear_dirty(unsigned long address, struct gmap *);
+
 
 void gmap_register_ipte_notifier(struct gmap_notifier *);
 void gmap_unregister_ipte_notifier(struct gmap_notifier *);
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 1ddf975352a0..ea4a31b95990 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -1401,6 +1401,27 @@ void s390_enable_skey(void)
 }
 EXPORT_SYMBOL_GPL(s390_enable_skey);
 
+/*
+ * Test and reset if a guest page is dirty
+ */
+bool gmap_test_and_clear_dirty(unsigned long address, struct gmap *gmap)
+{
+        pte_t *pte;
+        spinlock_t *ptl;
+        bool dirty = false;
+
+        pte = get_locked_pte(gmap->mm, address, &ptl);
+        if (unlikely(!pte))
+                return false;
+
+        if (ptep_test_and_clear_user_dirty(gmap->mm, address, pte))
+                dirty = true;
+
+        spin_unlock(ptl);
+        return dirty;
+}
+EXPORT_SYMBOL_GPL(gmap_test_and_clear_dirty);
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pmdp_clear_flush_young(struct vm_area_struct *vma, unsigned long address,
                            pmd_t *pmdp)