linux-kernel - Re: [PATCH v4 09/10] userfaultfd: update documentation to describe minor fault handling

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Date:   Thu, 4 Feb 2021 11:57:36 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Huang Ying <ying.huang@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Koutný <mkoutny@...e.com>,
        Michel Lespinasse <walken@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Xu <peterx@...hat.com>, Shaohua Li <shli@...com>,
        Shawn Anastasio <shawn@...stas.io>,
        Steven Rostedt <rostedt@...dmis.org>,
        Steven Price <steven.price@....com>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, Adam Ruprecht <ruprecht@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v4 09/10] userfaultfd: update documentation to describe
 minor fault handling

Hi Axel-

one typo found:

On 2/4/21 10:34 AM, Axel Rasmussen wrote:
> Reword / reorganize things a little bit into "lists", so new features /
> modes / ioctls can sort of just be appended.

Good plan.

> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> ---
>  Documentation/admin-guide/mm/userfaultfd.rst | 107 ++++++++++++-------
>  1 file changed, 66 insertions(+), 41 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
> index 65eefa66c0ba..cfd3daf59d0e 100644
> --- a/Documentation/admin-guide/mm/userfaultfd.rst
> +++ b/Documentation/admin-guide/mm/userfaultfd.rst

[snip]

> -
> -Once the ``userfaultfd`` has been enabled the ``UFFDIO_REGISTER`` ioctl should
> -be invoked (if present in the returned ``uffdio_api.ioctls`` bitmask) to
> -register a memory range in the ``userfaultfd`` by setting the
> +events, except page fault notifications, may be generated:
> +
> +- The ``UFFD_FEATURE_EVENT_*`` flags indicate that various other events
> +  other than page faults are supported. These events are described in more
> +  detail below in the `Non-cooperative userfaultfd`_ section.
> +
> +- ``UFFD_FEATURE_MISSING_HUGETLBFS`` and ``UFFD_FEATURE_MISSING_SHMEM``
> +  indicate that the kernel supports ``UFFDIO_REGISTER_MODE_MISSING``
> +  registrations for hugetlbfs and shared memory (covering all shmem APIs,
> +  i.e. tmpfs, ``IPCSHM``, ``/dev/zero``, ``MAP_SHARED``, ``memfd_create``,
> +  etc) virtual memory areas, respectively.
> +
> +- ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports
> +  ``UFFDIO_REGISTER_MODE_MINOR`` registration for hugetlbfs virtual memory
> +  areas.
> +
> +The userland application should set the feature flags it intends to use

(ah, userspace has moved to userland temporarily. :)

> +when envoking the ``UFFDIO_API`` ioctl, to request that those features be

        invoking

> +enabled if supported.


thanks.
-- 
~Randy