userfaultfd: non-cooperative: optimize mremap_userfaultfd_complete()

Optimize the mremap_userfaultfd_complete() interface to pass only the
vm_userfaultfd_ctx pointer through the stack as a microoptimization.

Link: http://lkml.kernel.org/r/20161216144821.5183-13-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/userfaultfd.c

@@ -608,11 +608,11 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
 	}
 }
 
-void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx vm_ctx,
+void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
 				 unsigned long from, unsigned long to,
 				 unsigned long len)
 {
-	struct userfaultfd_ctx *ctx = vm_ctx.ctx;
+	struct userfaultfd_ctx *ctx = vm_ctx->ctx;
 	struct userfaultfd_wait_queue ewq;
 
 	if (!ctx)

include/linux/userfaultfd_k.h

@@ -57,7 +57,7 @@ extern void dup_userfaultfd_complete(struct list_head *);
 
 extern void mremap_userfaultfd_prep(struct vm_area_struct *,
 				    struct vm_userfaultfd_ctx *);
-extern void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx,
+extern void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *,
 					unsigned long from, unsigned long to,
 					unsigned long len);
 
@@ -100,7 +100,7 @@ static inline void mremap_userfaultfd_prep(struct vm_area_struct *vma,
 {
 }
 
-static inline void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx ctx,
+static inline void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *ctx,
 					       unsigned long from,
 					       unsigned long to,
 					       unsigned long len)

mm/mremap.c

@@ -608,6 +608,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	up_write(&current->mm->mmap_sem);
 	if (locked && new_len > old_len)
 		mm_populate(new_addr + old_len, new_len - old_len);
-	mremap_userfaultfd_complete(uf, addr, new_addr, old_len);
+	mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
 	return ret;
 }