linux-kernel - Re: [PATCH v7 1/4] userfaultfd: Add UFFD WP Async support

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Date:   Wed, 25 Jan 2023 17:18:52 +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 v7 1/4] userfaultfd: Add UFFD WP Async support

On 1/24/23 10:26 PM, Peter Xu wrote:
> On Mon, Jan 23, 2023 at 03:11:20PM +0500, Muhammad Usama Anjum wrote:
>>> One thing worth mention is, I think for async wp it doesn't need to be
>>> restricted by UFFD_USER_MODE_ONLY, because comparing to the sync messages
>>> it has no risk of being utilized for malicious purposes.
>> I think with updated handling path updated in do_wp_page() and
>> wp_huge_pmd() in version, UFFD_USER_MODE_ONLY will not affect us.
> 
> This is more or less a comment for the design, the new code should work (by
> bypassing handle_userfaultfd(), where this bit was checked).
> 
> We'll need an man page update if this feature will be merged [1], and if so
> it'll need to be updated for the UFFD_USER_MODE_ONLY section regarding to
> async uffd-wp support too.  I think that can also be worked out after the
> series being accepted first, so just a heads up.
> 
> [1] https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
Thank you for explaining it. Definitely, we'll update the man pages after
the change has been merged. I've added it to my notes.>

-- 
BR,
Muhammad Usama Anjum