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Date:   Mon, 26 Apr 2021 19:23:57 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Axel Rasmussen <axelrasmussen@google.com>
cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Joe Perches <joe@perches.com>,
        Lokesh Gidra <lokeshgidra@google.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Peter Xu <peterx@redhat.com>, Shaohua Li <shli@fb.com>,
        Shuah Khan <shuah@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Wang Qing <wangqing@vivo.com>, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
        Brian Geffon <bgeffon@google.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Mina Almasry <almasrymina@google.com>,
        Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v4 04/10] userfaultfd/shmem: support minor fault registration
 for shmem
In-Reply-To: <20210420220804.486803-5-axelrasmussen@google.com>
Message-ID: <alpine.LSU.2.11.2104261920110.2998@eggly.anvils>
References: <20210420220804.486803-1-axelrasmussen@google.com> <20210420220804.486803-5-axelrasmussen@google.com>
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On Tue, 20 Apr 2021, Axel Rasmussen wrote:

> This patch allows shmem-backed VMAs to be registered for minor faults.
> Minor faults are appropriately relayed to userspace in the fault path,
> for VMAs with the relevant flag.
> 
> This commit doesn't hook up the UFFDIO_CONTINUE ioctl for shmem-backed
> minor faults, though, so userspace doesn't yet have a way to resolve
> such faults.
> 
> Acked-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>

And if this "04/10" had been numbered 03/10, I would have said
Acked-by: Hugh Dickins <hughd@google.com>

Just read the comment above: "so userspace doesn't yet have a way to
resolve such faults" - if it doesn't by this stage, we're in trouble.

> ---
>  fs/userfaultfd.c                 |  6 +++---
>  include/uapi/linux/userfaultfd.h |  7 ++++++-
>  mm/memory.c                      |  8 +++++---
>  mm/shmem.c                       | 12 +++++++++++-
>  4 files changed, 25 insertions(+), 8 deletions(-)