From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [PATCH XEN v8 24/29] tools/libs/call: linux: touch newly allocated pages after madvise lockdown Date: Tue, 19 Jan 2016 14:58:48 +0000 Message-ID: <20160119145848.GJ1691@citrix.com> References: <1452864168.32341.97.camel@citrix.com> <1452864188-2417-1-git-send-email-ian.campbell@citrix.com> <1452864188-2417-25-git-send-email-ian.campbell@citrix.com> <20160119132420.GZ1691@citrix.com> <569E4E3E.9060103@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <569E4E3E.9060103@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Roger Pau =?iso-8859-1?Q?Monn=E9?= Cc: ian.jackson@eu.citrix.com, Wei Liu , Ian Campbell , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Tue, Jan 19, 2016 at 03:54:54PM +0100, Roger Pau Monn=E9 wrote: > El 19/01/16 a les 14.24, Wei Liu ha escrit: > > On Fri, Jan 15, 2016 at 01:23:03PM +0000, Ian Campbell wrote: > >> This avoids a potential issue with a fork after allocation but before > >> madvise. > >> > >> Signed-off-by: Ian Campbell > >> --- > >> v7: New, replacing "tools/libs/call: linux: avoid forking between mmap > >> and madvise". > >> --- > >> tools/libs/call/linux.c | 14 +++++++++++++- > >> 1 file changed, 13 insertions(+), 1 deletion(-) > >> > >> diff --git a/tools/libs/call/linux.c b/tools/libs/call/linux.c > >> index 3641e41..651f380 100644 > >> --- a/tools/libs/call/linux.c > >> +++ b/tools/libs/call/linux.c > > = > > I didn't notice you only handled this for Linux until now. > > = > > I think FreeBSD and NetBSD need similar treatment, too? But then current > > BSD* code doesn't even support DONTFORK in madvise. > > = > > Adding Roger for more input. > = > Hm, right, thanks for noticing this. I don't think FreeBSD needs a > similar treatment (pre-faulting), because mlock will remove any CoW when > making the pages wired. > = > Also, AFAICT we don't need to call madvise or minherit(2) because > mlock(2) already takes care of preventing the memory region from being > copied to the child on fork: > = > "Locked mappings are not inherited by the child process after a > fork(2)." [0] > = > So I think we are safe on the FreeBSD side. > = But what if the process forks between mmap and mlock? I think that warrants touching the area like we do for Linux here. Wei. > Roger. > = > [0] https://www.freebsd.org/cgi/man.cgi?query=3Dmlock > =