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

From: Peter Xu <peterx@redhat.com>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Charan Teja Reddy <charante@codeaurora.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"Dmitry V . Levin" <ldv@altlinux.org>,
	Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
	Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
	Jonathan Corbet <corbet@lwn.net>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
	Shuah Khan <shuah@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, zhangyi <yi.zhang@huawei.com>,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control
Date: Tue, 26 Apr 2022 16:32:58 -0400	[thread overview]
Message-ID: <YmhW+mOuQUWsByj4@xz-m1.local> (raw)
In-Reply-To: <20220422212945.2227722-3-axelrasmussen@google.com>

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