2 files changed, 28 insertions, 1 deletions

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index eeaf8023851f..60acb93a4680 100644
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -115,7 +115,16 @@ static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
                 pmd = *pmdp;
                 barrier();
                 next = pmd_addr_end(addr, end);
-                if (pmd_none(pmd))
+                /*
+                 * The pmd_trans_splitting() check below explains why
+                 * pmdp_splitting_flush() has to serialize with
+                 * smp_call_function() against our disabled IRQs, to stop
+                 * this gup-fast code from running while we set the
+                 * splitting bit in the pmd. Returning zero will take
+                 * the slow path that will call wait_split_huge_page()
+                 * if the pmd is still in splitting state.
+                 */
+                if (pmd_none(pmd) || pmd_trans_splitting(pmd))
                         return 0;
                 if (unlikely(pmd_huge(pmd))) {
                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index b402991e43d7..a6131d1fe6c0 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -866,3 +866,21 @@ bool kernel_page_present(struct page *page)
         return cc == 0;
 }
 #endif /* CONFIG_HIBERNATION && CONFIG_DEBUG_PAGEALLOC */
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void pmdp_splitting_flush_sync(void *arg)
+{
+        /* Simply deliver the interrupt */
+}
+
+void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
+                          pmd_t *pmdp)
+{
+        VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+        if (!test_and_set_bit(_SEGMENT_ENTRY_SPLIT_BIT,
+                              (unsigned long *) pmdp)) {
+                /* need to serialize against gup-fast (IRQ disabled) */
+                smp_call_function(pmdp_splitting_flush_sync, NULL, 1);
+        }
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */