Re: [dpdk-dev] [PATCH 2/2] virtio: change io privilege level as early as possible

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 1 Oct 2015 07:25:45 -0400
Neil Horman <nhorman@tuxdriver.com> wrote:

> On Wed, Sep 30, 2015 at 05:37:05PM +0200, Thomas Monjalon wrote:
> > 2015-09-30 10:52, Neil Horman:
> > > On Wed, Sep 30, 2015 at 10:28:53AM +0200, David Marchand wrote:
> > > > On Tue, Sep 29, 2015 at 9:25 PM, Stephen Hemminger <
> > > > stephen@networkplumber.org> wrote:
> > > > 
> > > > > On Tue, 10 Mar 2015 09:14:28 -0400
> > > > > Neil Horman <nhorman@tuxdriver.com> wrote:
> > > > > > I don't see how this works for all cases.  The constructor is called
> > > > > once when
> > > > > > the library is first loaded.  What if you have multiple independent
> > > > > (i.e. not
> > > > > > forked children) processes that are using the dpdk in parallel?  Only the
> > > > > > process that triggered the library load will have io permissions set
> > > > > > appropriately.  I think what you need is to have every application that
> > > > > expects
> > > > > > to call through the transmit path or poll the receive path call iopl,
> > > > > which I
> > > > > > think speaks to having this requirement documented, so each application
> > > > > can call
> > > > > > iopl prior to calling fork/daemonize/etc.
> > > > > >
> > > > >
> > > > > I am still seeing this problem with DPDK 2.0 and 2.1.
> > > > > It seems to me that doing the iopl init in eal_init is the only safe way.
> > > > > Other workaround is to have application calling iopl_init before eal_init
> > > > > but that kind of violates the current method of all things being
> > > > > initialized by eal_init
> > > > 
> > > > Putting it in the virtio pmd constructor is my preferred solution and we
> > > > don't need to pollute the eal for virtio (specific to x86, btw).
> > > 
> > > Preferred solution or not, you can't just call iopl from the constructor,
> > > because not all process will get appropriate permissions.  It needs to be called
> > > by every process.  What Stephen is saying is that your solution has use cases
> > > for which it doesn't work, and that needs to be solved.
> > 
> > I think it may be solved by calling iopl in the constructor.
> > We just need an extra call in rte_virtio_pmd_init() to detect iopl failures.
> > We can also simply move rte_eal_intr_init() after rte_eal_dev_init().
> > Please read my previous post on this topic:
> > 	http://thread.gmane.org/gmane.comp.networking.dpdk.devel/14761/focus=22341
> > 
> > About the multiprocess case, I don't see the problem as the RX/TX and interrupt
> > threads are forked in the rte_eal_init() context which should call iopl even in
> > secondary processes.
> > 
> 
> I'm not talking about secondary processes here (i.e. processes forked from a
> parent that was the process which initialized the dpdk).  I'm referring to two
> completely independent processes, both of which link to and use the dpdk.
> 
> Though I think we're saying the same thing.  When you say 'constructor' above,
> you don't mean 'constructor' in the strict sense, but rather the pmd init
> routine (the one called from rte_eal_vdev_init and rte_eal_dev_init).  If this
> is the case, then yes, that works fine, since each process linking to the DPDK
> will enter those routines and call iopl.  In fact, if thats the case, then no
> call is needed in the constructor at all.

I think this patch should be rebased and resubmitted for 2.2.

It fixes a real problem (virtio link state). The driver changed directory
and the the patch could be redone to minimize changes.