mm: move use_mm/unuse_mm from aio.c to mm/

Anyone who wants to do copy to/from user from a kernel thread, needs
use_mm (like what fs/aio has).  Move that into mm/, to make reusing and
exporting easier down the line, and make aio use it.  Next intended user,
besides aio, will be vhost-net.

Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/mm/mmu_context.c b/mm/mmu_context.c
new file mode 100644
index 000000000000..fd473b51c903
--- /dev/null
+++ b/mm/mmu_context.c
@@ -0,0 +1,55 @@
+/* Copyright (C) 2009 Red Hat, Inc.
+ *
+ * See ../COPYING for licensing terms.
+ */
+
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+#include <linux/sched.h>
+
+#include <asm/mmu_context.h>
+
+/*
+ * use_mm
+ *      Makes the calling kernel thread take on the specified
+ *      mm context.
+ *      Called by the retry thread execute retries within the
+ *      iocb issuer's mm context, so that copy_from/to_user
+ *      operations work seamlessly for aio.
+ *      (Note: this routine is intended to be called only
+ *      from a kernel thread context)
+ */
+void use_mm(struct mm_struct *mm)
+{
+        struct mm_struct *active_mm;
+        struct task_struct *tsk = current;
+
+        task_lock(tsk);
+        active_mm = tsk->active_mm;
+        atomic_inc(&mm->mm_count);
+        tsk->mm = mm;
+        tsk->active_mm = mm;
+        switch_mm(active_mm, mm, tsk);
+        task_unlock(tsk);
+
+        mmdrop(active_mm);
+}
+
+/*
+ * unuse_mm
+ *      Reverses the effect of use_mm, i.e. releases the
+ *      specified mm context which was earlier taken on
+ *      by the calling kernel thread
+ *      (Note: this routine is intended to be called only
+ *      from a kernel thread context)
+ */
+void unuse_mm(struct mm_struct *mm)
+{
+        struct task_struct *tsk = current;
+
+        task_lock(tsk);
+        tsk->mm = NULL;
+        /* active_mm is still 'mm' */
+        enter_lazy_tlb(mm, tsk);
+        task_unlock(tsk);
+}