linux-kernel - Re: [PATCH v8 2/4] userfaultfd: split mwriteprotect

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Message-ID: <Y9QEdbkZxOJ10oEJ@x1n>
Date:   Fri, 27 Jan 2023 12:05:57 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <emmir@...gle.com>,
        Andrei Vagin <avagin@...il.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Yun Zhou <yun.zhou@...driver.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Alex Sierra <alex.sierra@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: Re: [PATCH v8 2/4] userfaultfd: split mwriteprotect_range()

On Tue, Jan 24, 2023 at 01:43:21PM +0500, Muhammad Usama Anjum wrote:
> Split mwriteprotect_range() to create a unlocked version. This
> will be used in the next patch to write protect a memory area.
> Add a helper function, wp_range_async() as well.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>

IIUC this patch is not needed.  You have a stable vma, so I think you can
directly use uffd_wp_range(), while most of the mwriteprotect_range() is
not needed.

There's one trivial detail of ignoring userfaultfd_ctx->mmap_changing when
it's set to true, but I don't think it applies here either because it was
used to resolve a problem in uffd non-cooperative mode on the predictable
behavior of events, here I don't think it matters a lot either.

-- 
Peter Xu