Date:   Tue, 24 Jan 2023 12:26:08 -0500
From:   Peter Xu <peterx@redhat.com>
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <emmir@google.com>,
        Andrei Vagin <avagin@gmail.com>,
        Danylo Mocherniuk <mdanylo@google.com>,
        Paul Gofman <pgofman@codeweavers.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>,
        Yun Zhou <yun.zhou@windriver.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Alex Sierra <alex.sierra@amd.com>,
        Matthew Wilcox <willy@infradead.org>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>, kernel@collabora.com
Subject: Re: [PATCH v7 1/4] userfaultfd: Add UFFD WP Async support
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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

-- 
Peter Xu