linux-kernel - Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control

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Date:   Tue, 26 Apr 2022 16:32:58 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Charan Teja Reddy <charante@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        zhangyi <yi.zhang@...wei.com>, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine
 grained access control

Axel,

On Fri, Apr 22, 2022 at 02:29:41PM -0700, Axel Rasmussen wrote:
> @@ -65,6 +66,8 @@ struct userfaultfd_ctx {
>  	unsigned int flags;
>  	/* features requested from the userspace */
>  	unsigned int features;
> +	/* whether or not to handle kernel faults */
> +	bool handle_kernel_faults;

Could you help explain why we need this bool?  I failed to figure out
myself on the difference against "!(ctx->flags & UFFD_USER_MODE_ONLY)".

Thanks,

-- 
Peter Xu