Re: [PATCH 5/6] userfaultfd: decouple fault reason from VMA flags

On Mon, Aug 24, 2026 at 04:46:14PM +0200, David Hildenbrand (Arm) wrote:

On 8/23/26 14:17, Mike Rapoport (Microsoft) wrote:

quoted

Introduce enum uffd_reason to define reasons for user faults rather than
overload VM_UFFD_* VMA flags for that.

Using a dedicated enum makes the code clearer and decoupling the fault
reason from VMA flags clears the way for moving the uffd mode bits out
of VMA namespace.

No functional change.

Assisted-by: copilot:claude-opus-4.6
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 include/linux/userfaultfd_k.h    | 16 ++++++++++++++--
 include/uapi/linux/userfaultfd.h |  6 +++---
 mm/huge_memory.c                 |  6 +++---
 mm/hugetlb.c                     | 10 +++++-----
 mm/memory.c                      | 10 +++++-----
 mm/shmem.c                       |  4 ++--
 mm/userfaultfd.c                 | 30 +++++++++++++++---------------
 7 files changed, 47 insertions(+), 35 deletions(-)

diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 45355bdb4ec7..f401623f315d 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h

@@ -9,6 +9,18 @@
 #ifndef _LINUX_USERFAULTFD_K_H
 #define _LINUX_USERFAULTFD_K_H
 
+#include <linux/bits.h>
+
+/* Fault reason #PF handler passes to handle_userfault() */
+enum uf_reason {

Can we just call this "userfault_reason" or "uffd_reason" ? Maybe the latter is
actually what we want?

userfault_reason sounds better to me.

It describes what kind of user fault we are handling and the 'fd' part has
nothing to do with it. 
We do use uffd as a short name for the subsystem, but still most if not all
userfaultfd "external" APIs use userfault_ prefix.

uf_ was an attempt to make it wee shorter :)
 

-- 
Cheers,
David

-- 
Sincerely yours,
Mike.