Re: [PATCH 3/3] hv_netvsc: Implement VF matching based on serial numbers

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 9 Dec 2016 20:09:49 +0000
Haiyang Zhang <haiyangz@microsoft.com> wrote:

> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Friday, December 9, 2016 1:21 PM
> > To: Greg KH <gregkh@linuxfoundation.org>
> > Cc: KY Srinivasan <kys@microsoft.com>; olaf@aepfle.de; Haiyang Zhang
> > <haiyangz@microsoft.com>; linux-kernel@vger.kernel.org;
> > bjorn.helgaas@gmail.com; apw@canonical.com; devel@linuxdriverproject.org;
> > leann.ogasawara@canonical.com; jasowang@redhat.com
> > Subject: Re: [PATCH 3/3] hv_netvsc: Implement VF matching based on
> > serial numbers
> > 
> > On Fri, 9 Dec 2016 08:31:22 +0100
> > Greg KH <gregkh@linuxfoundation.org> wrote:
> >   
> > > On Fri, Dec 09, 2016 at 12:05:53AM +0000, KY Srinivasan wrote:  
> > > >
> > > >  
> > > > > -----Original Message-----
> > > > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > > > Sent: Thursday, December 8, 2016 7:56 AM
> > > > > To: KY Srinivasan <kys@microsoft.com>
> > > > > Cc: linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
> > > > > olaf@aepfle.de; apw@canonical.com; vkuznets@redhat.com;
> > > > > jasowang@redhat.com; leann.ogasawara@canonical.com;
> > > > > bjorn.helgaas@gmail.com; Haiyang Zhang <haiyangz@microsoft.com>
> > > > > Subject: Re: [PATCH 3/3] hv_netvsc: Implement VF matching based on  
> > serial  
> > > > > numbers
> > > > >
> > > > > On Thu, Dec 08, 2016 at 12:33:43AM -0800,  
> > kys@exchange.microsoft.com  
> > > > > wrote:  
> > > > > > From: Haiyang Zhang <haiyangz@microsoft.com>
> > > > > >
> > > > > > We currently use MAC address to match VF and synthetic NICs.  
> > Hyper-V  
> > > > > > provides a serial number to both devices for this purpose. This  
> > patch  
> > > > > > implements the matching based on VF serial numbers. This is the  
> > way  
> > > > > > specified by the protocol and more reliable.
> > > > > >
> > > > > > Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> > > > > > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> > > > > > ---
> > > > > >  drivers/net/hyperv/netvsc_drv.c |   55  
> > > > > ++++++++++++++++++++++++++++++++++++---  
> > > > > >  1 files changed, 51 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/net/hyperv/netvsc_drv.c  
> > > > > b/drivers/net/hyperv/netvsc_drv.c  
> > > > > > index 9522763..c5778cf 100644
> > > > > > --- a/drivers/net/hyperv/netvsc_drv.c
> > > > > > +++ b/drivers/net/hyperv/netvsc_drv.c
> > > > > > @@ -1165,9 +1165,10 @@ static void netvsc_free_netdev(struct  
> > > > > net_device *netdev)  
> > > > > >  	free_netdev(netdev);
> > > > > >  }
> > > > > >
> > > > > > -static struct net_device *get_netvsc_bymac(const u8 *mac)
> > > > > > +static struct net_device *get_netvsc_byvfser(u32 vfser)
> > > > > >  {
> > > > > >  	struct net_device *dev;
> > > > > > +	struct net_device_context *ndev_ctx;
> > > > > >
> > > > > >  	ASSERT_RTNL();
> > > > > >
> > > > > > @@ -1175,7 +1176,8 @@ static void netvsc_free_netdev(struct  
> > net_device  
> > > > > *netdev)  
> > > > > >  		if (dev->netdev_ops != &device_ops)
> > > > > >  			continue;	/* not a netvsc device */
> > > > > >
> > > > > > -		if (ether_addr_equal(mac, dev->perm_addr))
> > > > > > +		ndev_ctx = netdev_priv(dev);
> > > > > > +		if (ndev_ctx->vf_serial == vfser)
> > > > > >  			return dev;
> > > > > >  	}
> > > > > >
> > > > > > @@ -1205,21 +1207,66 @@ static void netvsc_free_netdev(struct  
> > > > > net_device *netdev)  
> > > > > >  	return NULL;
> > > > > >  }
> > > > > >
> > > > > > +static u32 netvsc_get_vfser(struct net_device *vf_netdev)
> > > > > > +{
> > > > > > +	struct device *dev;
> > > > > > +	struct hv_device *hdev;
> > > > > > +	struct hv_pcibus_device *hbus = NULL;
> > > > > > +	struct list_head *iter;
> > > > > > +	struct hv_pci_dev *hpdev;
> > > > > > +	unsigned long flags;
> > > > > > +	u32 vfser = 0;
> > > > > > +	u32 count = 0;
> > > > > > +
> > > > > > +	for (dev = &vf_netdev->dev; dev; dev = dev->parent) {  
> > > > >
> > > > > You are going to walk the whole device tree backwards?  That's  
> > crazy.  
> > > > > And foolish.  And racy and broken (what happens if the tree  
> > changes  
> > > > > while you do this?)  Where is the lock being grabbed while this  
> > happens?  
> > > > > What about reference counts?  Do you see other drivers ever doing  
> > this  
> > > > > (if you do, point them out and I'll go yell at them too...)  
> > > >
> > > > Greg,
> > > >
> > > > We are registering for netdev events. Coming into this function, the  
> > caller  
> > > > guarantees that the list of netdevs does not change - we assert this  
> > on entry:  
> > > > ASSERT_RTNL(). We are only walking up the device tree for the  
> > netdevs whose  
> > > > state change is being notified to us - the device tree being walked  
> > here is limited to  
> > > > netdevs under question.  
> > >
> > > But a netdev is a child of some type of "real" device, and you are now
> > > walking the tree of all devices up to the "root" parent device, which
> > > means you will hit PCI bridges, USB controllers, and all sorts of fun
> > > things if you are a child of those types of devices.
> > >
> > > And can't you tell if the netdev for this event, really is "your"
> > > netdev?  Or are you getting called this for "all" netdevs?  Sorry, I
> > > don't know this api, any pointers to it would be appreciated.
> > >  
> > > > We have a reference to the device and we know the device is not  
> > going away. Is it not  
> > > > safe to dereference the parent pointer - after all the child has  
> > taken a reference on  
> > > > the parent as part of  device_add() call.  
> > >
> > > It might be, and might not be.  There's a reason you don't see this
> > > pattern anywhere in the kernel because of this...
> > >  
> > > > > > +		if (!dev_is_vmbus(dev))
> > > > > > +			continue;  
> > > > >
> > > > > Ick.
> > > > >
> > > > > Why isn't your parent pointer a vmbus device all the time?  How  
> > could  
> > > > > you get burried down in the device hierarchy when you are the  
> > driver for  
> > > > > a specific bus type in the first place?  How could this function  
> > ever be  
> > > > > called for a device that is NOT of this type?  
> > > >
> > > > We get notified when state changes on any of the netdev devices in  
> > the system.  
> > > > Not all netdevs in the system belong to vmbus. Consider for instance  
> > the  
> > > > emulated NIC that can be configured. This is an emulated PCI NIC. We  
> > are only  
> > > > interested in netdevs that correspond to the VF instance that we are  
> > interested in.  
> > >
> > > Can you "know" this is your netdev by some other way than having to  
> > walk  
> > > the device tree?  Name?  local device type?  Something else?  This  
> > seems  
> > > like an odd api in that everyone would have to do gyrations like this  
> > in  
> > > order to determine if the netdev is "theirs" or not...  
> > 
> > The scenario is SR-IOV on Hyper-V. In the case of VF device, the host
> > hands the
> > guest OS a PCI device for the virtual function device. The VF device is
> > placed
> > on a special synthetic PCI bus (ie not part of the other buses on the
> > system).
> > The VF device also has a synthetic network interface (netvsc) which
> > lives
> > on VMBUS.  This code is about managing the interaction between the two.
> > 
> > The association between VF and synthetic NIC is done in response to the
> > VF network device being registered. Initial version was based on MAC
> > address
> > which is the same.  Later refinement used permanent MAC address to
> > avoid bugs if MAC address changed.  This version is to use serial number
> > instead which is safer than MAC address.
> > 
> > The code to walk up/down maybe not be needed to find serial number.
> > Perhaps a more direct single set of conditions is possible?
> > 
> > Something like:
> > 
> > In pci-hyperv.c
> > 
> > u32 hv_pcifront_get_serial(struct pci_bus *bus, unsigned int devfn)
> > {
> > 	struct hv_pcibus_device *hbus
> > 		= container_of(bus->sysdata,
> > 			       struct hv_pcibus_device, sysdata);
> > 	struct hf_pci_dev *hpdev;
> > 	u32 serial;
> > 
> > 	hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
> > 	if (!hpdev)
> > 		return 0;
> > 
> > 	serial = hpdev->devs.ser;
> > 	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
> > 	return serial;
> > }
> > 
> > In netvsc_drv.c
> > 
> > static u32 netvsc_get_vfser(struct net_device *vf_netdev)
> > {
> > 	struct device *dev = vf_netdev->dev.parent;
> > 	struct pci_dev *pdev;
> > 	u32 wslot;
> > 
> > 	if (!dev || !dev_is_pci(dev))
> > 		return 0;
> > 
> > 	pdev = container_of(dev, struct pci_device, dev);
> > 
> > 	return hv_pcifront_get_serial(pdev->bus, pdev->devfn);
> > }
> > 
> > 
> > 
> > 
> > 
> > P.S: it would be good to be able to get win_slot out through sysfs as
> > well for systemd/udev.  
> 
> Stephen,
> 
> Thanks for suggestion. Actually, in my earlier implementation of this 
> feature (VF serial based matching), I thought about export a function
> from vPCI driver, then calling it from netvsc. So I don't need to 
> move structs between headers... But, it creates a dependency of netvsc
> on vPCI driver's symbol. So, even if on a VM without SRIOV, we have to
> load vPCI driver, which we don't want.
> 
> Also, hv_vpci device is 3 parent layers above the vf_netdevice:
> Here is the VF drv hierarchy --
> Should we assume it's always 3 parents above vf_netdevice, or search for it?
> 
> [  368.185259] HZINFO:NETDEV_REGISTER:
> [  368.185261] HZINFO: dev:ffff88007c10d518, bus:          (null), busName:(null), drvName:(null)
> [  368.185262] HZINFO: dev:ffff88007c10c0a0, bus:ffffffff81ce4b60, busName:pci, drvName:ixgbevf
> [  368.185263] HZINFO: dev:ffff8800355c0000, bus:          (null), busName:(null), drvName:(null)
> [  368.185264] HZINFO: dev:ffff8800355c5428, bus:ffffffffa0008160, busName:vmbus, drvName:hv_pci
> [  368.185264] HZINFO: dev:ffff88007c49e268, bus:ffffffff81ce9800, busName:acpi, drvName:vmbus
> [  368.185265] HZINFO: dev:ffff88007c48ea68, bus:ffffffff81ce9800, busName:acpi, drvName:(null)
> [  368.185266] HZINFO: dev:ffff88007c48aa68, bus:ffffffff81ce9800, busName:acpi, drvName:(null)
> [  368.185266] HZINFO: dev:ffff88007c48a268, bus:ffffffff81ce9800, busName:acpi, drvName:(null)
> [  368.185267] HZINFO: dev:ffff88007c489a68, bus:ffffffff81ce9800, busName:acpi, drvName:(null)
> 
> Thanks,
> - Haiyang

Since this is a synthetic bus, the topology should not change unless host side
software changes. The vf_netdev device has to be PCI device, so that is going to
be certain.  After that there maybe intermediate up to hv_pci. The code in hyperv-pci
already has similar stuff (ie for read_config).