1 files changed, 15 insertions, 28 deletions

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 4f74d94c8d97..5465b8613944 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -11,39 +11,26 @@
 #include <linux/sched.h>
 
 /*
- * best effort, GUP based copy_from_user() that is NMI-safe
+ * We rely on the nested NMI work to allow atomic faults from the NMI path; the
+ * nested NMI paths are careful to preserve CR2.
  */
 unsigned long
 copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 {
-        unsigned long offset, addr = (unsigned long)from;
-        unsigned long size, len = 0;
-        struct page *page;
-        void *map;
-        int ret;
+        unsigned long ret;
 
         if (__range_not_ok(from, n, TASK_SIZE))
-                return len;
-
-        do {
-                ret = __get_user_pages_fast(addr, 1, 0, &page);
-                if (!ret)
-                        break;
-
-                offset = addr & (PAGE_SIZE - 1);
-                size = min(PAGE_SIZE - offset, n - len);
-
-                map = kmap_atomic(page);
-                memcpy(to, map+offset, size);
-                kunmap_atomic(map);
-                put_page(page);
-
-                len  += size;
-                to   += size;
-                addr += size;
-
-        } while (len < n);
-
-        return len;
+                return 0;
+
+        /*
+         * Even though this function is typically called from NMI/IRQ context
+         * disable pagefaults so that its behaviour is consistent even when
+         * called form other contexts.
+         */
+        pagefault_disable();
+        ret = __copy_from_user_inatomic(to, from, n);
+        pagefault_enable();
+
+        return n - ret;
 }
 EXPORT_SYMBOL_GPL(copy_from_user_nmi);