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

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 10 Mar 2015 09:14:28 -0400
Neil Horman <nhorman@tuxdriver.com> wrote:

> On Mon, Mar 09, 2015 at 03:56:39PM +0100, David Marchand wrote:
> > Playing with virtio link status triggers a segfault because of an incorrect io
> > privilege level.
> > 
> > To reproduce the problem, virtio device must be bound to igb_uio to have lsc
> > enabled.
> > 
> > $ lspci |grep Ethernet
> > 00:03.0 Ethernet controller: Red Hat, Inc Virtio network device
> > $ modprobe uio
> > $ insmod ./x86_64-native-linuxapp-gcc/kmod/igb_uio.ko
> > $ echo 0000:00:03.0 > /sys/bus/pci/devices/0000\:00\:03.0/driver/unbind
> > $ echo 1af4 1000 > /sys/bus/pci/drivers/igb_uio/new_id
> > $ ./x86_64-native-linuxapp-gcc/app/testpmd -c 0x6 -n 3 -w 0000:00:03.0 -- -i --txqflags=0xf01
> > [snip]
> > EAL: PCI device 0000:00:03.0 on NUMA socket -1
> > EAL:   probe driver: 1af4:1000 rte_virtio_pmd
> > Interactive-mode selected
> > Configuring Port 0 (socket 0)
> > Port 0: DE:AD:DE:01:02:03
> > Checking link statuses...
> > Port 0 Link Up - speed 10000 Mbps - full-duplex
> > Done
> > testpmd>
> > 
> > Then, from qemu monitor:
> > (qemu) set_link virtio-net-pci.0 off
> > 
> > testpmd> Segmentation fault
> > 
> > A call to rte_eal_iopl_init() in a specific constructor has been added so that,
> > on Linux, iopl() is called asap:
> > - for statically linked virtio pmd, the constructor will be called at binary
> >   start,
> > - for shared virtio pmd (loaded using -d eal option), it will be called at
> >   dlopen() in rte_eal_init().
> > 
> > On linux, iopl() effects are inherited by children threads, so calling it in a
> > constructor will ensure that any thread / process created after rte_eal_init()
> > inherits the io privilege level needed by the pmd.
> > 
> > We keep call to rte_eal_iopl_init() in the pmd init macro so that the pmd will
> > not register if the io privilege level is insufficient.
> > 
> > Besides, I moved rte_virtio_pmd_init() and related structure near its calling
> > site, so that all init code can be looked at in a glance.
> > The only change here is a new comment.
> > 
> > Signed-off-by: David Marchand <david.marchand@6wind.com>
> > ---
> >  lib/librte_pmd_virtio/virtio_ethdev.c |   71 ++++++++++++++++++++-------------
> >  1 file changed, 43 insertions(+), 28 deletions(-)
> > 
> > diff --git a/lib/librte_pmd_virtio/virtio_ethdev.c b/lib/librte_pmd_virtio/virtio_ethdev.c
> > index d239083..29332fa 100644
> > --- a/lib/librte_pmd_virtio/virtio_ethdev.c
> > +++ b/lib/librte_pmd_virtio/virtio_ethdev.c
> > @@ -1228,34 +1228,6 @@ eth_virtio_dev_init(__rte_unused struct eth_driver *eth_drv,
> >  	return 0;
> >  }
> >  
> > -static struct eth_driver rte_virtio_pmd = {
> > -	{
> > -		.name = "rte_virtio_pmd",
> > -		.id_table = pci_id_virtio_map,
> > -	},
> > -	.eth_dev_init = eth_virtio_dev_init,
> > -	.dev_private_size = sizeof(struct virtio_hw),
> > -};
> > -
> > -/*
> > - * Driver initialization routine.
> > - * Invoked once at EAL init time.
> > - * Register itself as the [Poll Mode] Driver of PCI virtio devices.
> > - * Returns 0 on success.
> > - */
> > -static int
> > -rte_virtio_pmd_init(const char *name __rte_unused,
> > -		    const char *param __rte_unused)
> > -{
> > -	if (rte_eal_iopl_init() != 0) {
> > -		PMD_INIT_LOG(ERR, "IOPL call failed - cannot use virtio PMD");
> > -		return -1;
> > -	}
> > -
> > -	rte_eth_driver_register(&rte_virtio_pmd);
> > -	return 0;
> > -}
> > -
> >  /*
> >   * Only 1 queue is supported, no queue release related operation
> >   */
> > @@ -1484,6 +1456,49 @@ __rte_unused uint8_t is_rx)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * Early init function, this is needed so that iopl() on linux is done before
> > + * rte_eal_init (since it creates other threads that must inherit from the one
> > + * that calls rte_eal_init).
> > + */
> > +static void __attribute__((constructor, used))
> > +rte_virtio_early_init(void)
> > +{
> > +	/* return value is checked at pmd init time, no need to check here, see
> > +	 * below. */
> > +	rte_eal_iopl_init();
> > +}
> > +
> 
> 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.
> 
> Neil

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