3 files changed, 61 insertions, 3 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3cccd053850f..3172a1c0f08e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -988,6 +988,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                         struct page **pages);
 struct page *get_dump_page(unsigned long addr);
+extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
+                            unsigned long address, unsigned int fault_flags);
 
 extern int try_to_release_page(struct page * page, gfp_t gfp_mask);
 extern void do_invalidatepage(struct page *page, unsigned long offset);
diff --git a/kernel/futex.c b/kernel/futex.c
index 3fbc76cbb9aa..0a308970c24a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -355,8 +355,8 @@ static int fault_in_user_writeable(u32 __user *uaddr)
         int ret;
 
         down_read(&mm->mmap_sem);
-        ret = get_user_pages(current, mm, (unsigned long)uaddr,
-                             1, 1, 0, NULL, NULL);
+        ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
+                               FAULT_FLAG_WRITE);
         up_read(&mm->mmap_sem);
 
         return ret < 0 ? ret : 0;
diff --git a/mm/memory.c b/mm/memory.c
index 3c9f3aa8332e..a56e3ba816b2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1805,7 +1805,63 @@ next_page:
 }
 EXPORT_SYMBOL(__get_user_pages);
 
-/**
+/*
+ * fixup_user_fault() - manually resolve a user page fault
+ * @tsk:        the task_struct to use for page fault accounting, or
+ *              NULL if faults are not to be recorded.
+ * @mm:         mm_struct of target mm
+ * @address:    user address
+ * @fault_flags:flags to pass down to handle_mm_fault()
+ *
+ * This is meant to be called in the specific scenario where for locking reasons
+ * we try to access user memory in atomic context (within a pagefault_disable()
+ * section), this returns -EFAULT, and we want to resolve the user fault before
+ * trying again.
+ *
+ * Typically this is meant to be used by the futex code.
+ *
+ * The main difference with get_user_pages() is that this function will
+ * unconditionally call handle_mm_fault() which will in turn perform all the
+ * necessary SW fixup of the dirty and young bits in the PTE, while
+ * handle_mm_fault() only guarantees to update these in the struct page.
+ *
+ * This is important for some architectures where those bits also gate the
+ * access permission to the page because they are maintained in software.  On
+ * such architectures, gup() will not be enough to make a subsequent access
+ * succeed.
+ *
+ * This should be called with the mm_sem held for read.
+ */
+int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
+                     unsigned long address, unsigned int fault_flags)
+{
+        struct vm_area_struct *vma;
+        int ret;
+
+        vma = find_extend_vma(mm, address);
+        if (!vma || address < vma->vm_start)
+                return -EFAULT;
+
+        ret = handle_mm_fault(mm, vma, address, fault_flags);
+        if (ret & VM_FAULT_ERROR) {
+                if (ret & VM_FAULT_OOM)
+                        return -ENOMEM;
+                if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
+                        return -EHWPOISON;
+                if (ret & VM_FAULT_SIGBUS)
+                        return -EFAULT;
+                BUG();
+        }
+        if (tsk) {
+                if (ret & VM_FAULT_MAJOR)
+                        tsk->maj_flt++;
+                else
+                        tsk->min_flt++;
+        }
+        return 0;
+}
+
+/*
  * get_user_pages() - pin user pages in memory
  * @tsk:        the task_struct to use for page fault accounting, or
  *              NULL if faults are not to be recorded.