s390/mm: implement __get_user_pages_fast()

This patch introduces the __get_user_pages_fast() function on s390,
which will be needed with CONFIG_TRANSPARENT_HUGEPAGE and futex.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 65cb06e2af4e..eeaf8023851f 100644
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -154,6 +154,43 @@ static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
         return 1;
 }
 
+/*
+ * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
+ * back to the regular GUP.
+ */
+int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
+                          struct page **pages)
+{
+        struct mm_struct *mm = current->mm;
+        unsigned long addr, len, end;
+        unsigned long next, flags;
+        pgd_t *pgdp, pgd;
+        int nr = 0;
+
+        start &= PAGE_MASK;
+        addr = start;
+        len = (unsigned long) nr_pages << PAGE_SHIFT;
+        end = start + len;
+        if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+                                        (void __user *)start, len)))
+                return 0;
+
+        local_irq_save(flags);
+        pgdp = pgd_offset(mm, addr);
+        do {
+                pgd = *pgdp;
+                barrier();
+                next = pgd_addr_end(addr, end);
+                if (pgd_none(pgd))
+                        break;
+                if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
+                        break;
+        } while (pgdp++, addr = next, addr != end);
+        local_irq_restore(flags);
+
+        return nr;
+}
+
 /**
  * get_user_pages_fast() - pin user pages in memory
  * @start:      starting user address