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

[David Hildenbrand (Arm)]

On 8/27/26 09:49, Mike Rapoport wrote:
> On Mon, Aug 24, 2026 at 04:46:14PM +0200, David Hildenbrand (Arm) wrote:
>> On 8/23/26 14:17, Mike Rapoport (Microsoft) wrote:
>>> 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@xxxxxxxxxx>
>>> ---
>>>  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 :)

Yeah, I got that; while uffd is a known acronym, the uf_ not so much (and also I
wouldn't suggest it to become a thing, lol :) )

I've been wondering for a while whether it really should be called

	handle_userfault()

And not instead

	handle_userfaultfd()

Or maybe even better

	handle_uffd_fault()

And then have

	uffd_fault_reason

... but just a thought.

-- 
Cheers,

David