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

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Message-ID: <c3cc49b6-1ad3-f5aa-50bb-a12f3bbb377a@collabora.com>
Date:   Mon, 30 Jan 2023 14:10:11 +0500
From:   Muhammad Usama Anjum <usama.anjum@...labora.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        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 1/27/23 10:05 PM, Peter Xu wrote:
> 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.
> 
Thanks, I'll drop this patch and do direct wiring to uffd_wp_range().

-- 
BR,
Muhammad Usama Anjum