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

From: Haiyang Zhang
Date: Fri Dec 09 2016 - 17:42:40 EST

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> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@xxxxxxxxxxxxxxxxxx]
> Sent: Friday, December 9, 2016 1:21 PM
> To: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: KY Srinivasan <kys@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> bjorn.helgaas@xxxxxxxxx; apw@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> leann.ogasawara@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx
> 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@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Fri, Dec 09, 2016 at 12:05:53AM +0000, KY Srinivasan wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx]
> > > > Sent: Thursday, December 8, 2016 7:56 AM
> > > > To: KY Srinivasan <kys@xxxxxxxxxxxxx>
> > > > Cc: linux-kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> > > > olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; vkuznets@xxxxxxxxxx;
> > > > jasowang@xxxxxxxxxx; leann.ogasawara@xxxxxxxxxxxxx;
> > > > bjorn.helgaas@xxxxxxxxx; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > > > 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@xxxxxxxxxxxxxxxxxxxxxx
> > > > wrote:
> > > > > From: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > > > >
> > > > > 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@xxxxxxxxxxxxx>
> > > > > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> > > > > ---
> > > > > 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

Next message: Vaibhav Shankar: "[PATCH] PCI: pciehp: Optimize PCIe root resume time"
Previous message: Rob Herring: "Re: [PATCH v3 1/6] mfd: dt: Fix "indicates" typo in mfd bindings document"
In reply to: Stephen Hemminger: "Re: [PATCH 3/3] hv_netvsc: Implement VF matching based on serial numbers"
Next in thread: Stephen Hemminger: "Re: [PATCH 3/3] hv_netvsc: Implement VF matching based on serial numbers"
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