Re: [Xen-devel] [PATCH XEN v8 24/29] tools/libs/call: linux: touch newly allocated pages after madvise lockdown

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jan 19, 2016 at 01:40:55PM +0000, Ian Campbell wrote:
> On Tue, 2016-01-19 at 13:24 +0000, Wei Liu wrote:
> > 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 <ian.campbell@xxxxxxxxxx>
> > > ---
> > > 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.
> 
> I think any updates to the *BSD side should come as separate improvements.
> 
> If they are necessary at all, the Linux stuff comes from Linux making use
> of particular behaviours on mlock()'s memory (specifically, IIRC, doing
> things such as THP and NUMA balancing which can cause page faults on the
> mlock'd pages despite them being locked) which are (possibly) allowed by
> POSIX, but *BSD may not take the same interpretation.
> 
> > Adding Roger for more input.
> > 
> > The changes in this patch look fine to me.
> 
> May I take that as an Ack?
> 

Yes.

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