1 files changed, 9 insertions, 1 deletions

diff --git a/include/asm-um/mmu_context.h b/include/asm-um/mmu_context.h
index 095bb627b96a..2edb4f1f789c 100644
--- a/include/asm-um/mmu_context.h
+++ b/include/asm-um/mmu_context.h
@@ -20,7 +20,15 @@ extern void force_flush_all(void);
 
 static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
 {
-        if (old != new)
+        /*
+         * This is called by fs/exec.c and fs/aio.c. In the first case, for an
+         * exec, we don't need to do anything as we're called from userspace
+         * and thus going to use a new host PID. In the second, we're called
+         * from a kernel thread, and thus need to go doing the mmap's on the
+         * host. Since they're very expensive, we want to avoid that as far as
+         * possible.
+         */
+        if (old != new && (current->flags & PF_BORROWED_MM))
                 force_flush_all();
 }