[PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance

Michael S. Tsirkin
Thu, 03 Dec 2020 10:44:17 -0000

On Thu, Dec 03, 2020 at 08:49:28AM +0200, Eli Cohen
wrote:
> On Wed, Dec 02, 2020 at 05:00:22PM -0500, Michael S. Tsirkin wrote:
> > On Wed, Dec 02, 2020 at 09:48:25PM +0800, Jason Wang wrote:
> > >
> > > On 2020/12/2 ??5:23, Michael S. Tsirkin wrote:
> > > > On Wed, Dec 02, 2020 at 07:57:14AM +0200, Eli Cohen wrote:
> > > > > On Wed, Dec 02, 2020 at 12:18:36PM +0800, Jason Wang
wrote:
> > > > > > On 2020/12/1 ??5:23, Cindy Lu wrote:
> > > > > > > On Mon, Nov 30, 2020 at 11:33 PM Michael S.
Tsirkin<mst at redhat.com>  wrote:
> > > > > > > > On Mon, Nov 30, 2020 at 06:41:45PM
+0800, Cindy Lu wrote:
> > > > > > > > > On Mon, Nov 30, 2020 at 5:33 PM
Michael S. Tsirkin<mst at redhat.com>  wrote:
> > > > > > > > > > On Mon, Nov 30, 2020 at
11:27:59AM +0200, Eli Cohen wrote:
> > > > > > > > > > > On Mon, Nov 30, 2020 at
04:00:51AM -0500, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Mon, Nov 30, 2020
at 08:27:46AM +0200, Eli Cohen wrote:
> > > > > > > > > > > > > On Sun, Nov 29,
2020 at 03:08:22PM -0500, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > On Sun,
Nov 29, 2020 at 08:43:51AM +0200, Eli Cohen wrote:
> > > > > > > > > > > > > > > We
should not try to use the VF MAC address as that is used by the
> > > > > > > > > > > > > > >
regular (e.g. mlx5_core) NIC implementation. Instead, use a random
> > > > > > > > > > > > > > >
generated MAC address.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > >
Suggested by: Cindy Lu<lulu at redhat.com>
> > > > > > > > > > > > > > >
Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5
devices")
> > > > > > > > > > > > > > >
Signed-off-by: Eli Cohen<elic at nvidia.com>
> > > > > > > > > > > > > > I
didn't realise it's possible to use VF in two ways
> > > > > > > > > > > > > > with and
without vdpa.
> > > > > > > > > > > > > Using a VF you
can create quite a few resources, e.g. send queues
> > > > > > > > > > > > > recieve queues,
virtio_net queues etc. So you can possibly create
> > > > > > > > > > > > > several
instances of vdpa net devices and nic net devices.
> > > > > > > > > > > > >
> > > > > > > > > > > > > > Could you
include a bit more description on the failure
> > > > > > > > > > > > > > mode?
> > > > > > > > > > > > > Well, using the
MAC address of the nic vport is wrong since that is the
> > > > > > > > > > > > > MAC of the
regular NIC implementation of mlx5_core.
> > > > > > > > > > > > Right but ATM it
doesn't coexist with vdpa so what's the problem?
> > > > > > > > > > > >
> > > > > > > > > > > This call is wrong:
mlx5_query_nic_vport_mac_address()
> > > > > > > > > > >
> > > > > > > > > > > > > > Is
switching to a random mac for such an unusual
> > > > > > > > > > > > > >
configuration really justified?
> > > > > > > > > > > > > Since I
can't use the NIC's MAC address, I have two options:
> > > > > > > > > > > > > 1. To get the
MAC address as was chosen by the user administering the
> > > > > > > > > > > > >      NIC. This
should invoke the set_config callback. Unfortunately this
> > > > > > > > > > > > >      is not
implemented yet.
> > > > > > > > > > > > >
> > > > > > > > > > > > > 2. Use a random
MAC address. This is OK since if (1) is implemented it
> > > > > > > > > > > > >      can always
override this random configuration.
> > > > > > > > > > > > >
> > > > > > > > > > > > > > It looks
like changing a MAC could break some guests,
> > > > > > > > > > > > > > can it
not?
> > > > > > > > > > > > > >
> > > > > > > > > > > > > No, it will
not. The current version of mlx5 VDPA does not allow regular
> > > > > > > > > > > > > NIC driver and
VDPA to co-exist. I have patches ready that enable that
> > > > > > > > > > > > > from steering
point of view. I will post them here once other patches on
> > > > > > > > > > > > > which they
depend will be merged.
> > > > > > > > > > > > >
> > > > > > > > > > > > >
https://patchwork.ozlabs.org/project/netdev/patch/20201120230339.651609-12-saeedm
at nvidia.com/
> > > > > > > > > > > > Could you be more
explicit on the following points:
> > > > > > > > > > > > - which
configuration is broken ATM (as in, two device have identical
> > > > > > > > > > > >     macs? any other
issues)?
> > > > > > > > > > > The only wrong thing is
the call to  mlx5_query_nic_vport_mac_address().
> > > > > > > > > > > It's not breaking
anything yet is wrong. The random MAC address setting
> > > > > > > > > > > is required for the
steering patches.
> > > > > > > > > > Okay so I'm not sure the
Fixes tag at least is appropriate if it's a
> > > > > > > > > > dependency of a new feature.
> > > > > > > > > >
> > > > > > > > > > > > - why won't
device MAC change from guest point of view?
> > > > > > > > > > > >
> > > > > > > > > > > It's lack of
implementation in qemu as far as I know.
> > > > > > > > > > Sorry not sure I understand.
What's not implemented in QEMU?
> > > > > > > > > >
> > > > > > > > > HI Michael, there are some bug in
qemu to set_config, this will fix in future,
> > > > > > > > > But this patch is still needed,
because without this patch the mlx
> > > > > > > > > driver will give an 0 mac address
to qemu
> > > > > > > > > and qemu will overwrite the default
mac address.  This will cause traffic down.
> > > > > > > > Hmm the patch description says VF mac
address, not 0 address. Confused.
> > > > > > > > If there's no mac we can clear
VIRTIO_NET_F_MAC and have guest
> > > > > > > > use a random value ...
> > > > > > I'm not sure this can work for all types of
vDPA (e.g it could not be a
> > > > > > learning bridge in the swtich).
> > > > > >
> > > > > >
> > > > > > > hi Michael?
> > > > > > > I have tried as your suggestion, seems even
remove the
> > > > > > > VIRTIO_NET_F_MAC the qemu will still call
get_cinfig and overwrite the
> > > > > > > default address in  VM,
> > > > > > This looks a bug in qemu, in guest driver we had:
> > > > > >
> > > > > >  ??? /* Configuration may specify what MAC to
use.? Otherwise random. */
> > > > > >  ??? if (virtio_has_feature(vdev,
VIRTIO_NET_F_MAC))
> > > > > >  ??? ??? virtio_cread_bytes(vdev,
> > > > > >  ??? ??? ??? ??? ?? offsetof(struct
virtio_net_config, mac),
> > > > > >  ??? ??? ??? ??? ?? dev->dev_addr,
dev->addr_len);
> > > > > >  ??? else
> > > > > >  ??? ??? eth_hw_addr_random(dev);
> > > > > >
> > > > > >
> > > > > > > this process is like
> > > > > > > vdpa _init -->qemu call get_config
->mlx driver will give  an mac
> > > > > > > address with all 0-->
> > > > > > > qemu will not check this mac address and use
it --> overwrite the mac
> > > > > > > address in qemu
> > > > > > >
> > > > > > > So for my understanding there are several
method to fix this problem
> > > > > > >
> > > > > > > 1, qemu check the mac address, if the mac
address is all 0, qemu will
> > > > > > > ignore it and set the random mac address to
mlx driver.
> > > > > > So my understanding is that, if mac address is all
0, vDPA parent should not
> > > > > > advertise VIRTIO_NET_F_MAC. And qemu should
emulate this feature as you did:
> > > > > Thinking it over, at least in mlx5, I should always
advertise
> > > > > VIRTIO_NET_F_MAC and set a non zero MAC value. The
source of the MAC can
> > > > > be either randomly generated value by mlx5_vdpa or by a
management tool.
> > > > > This is important becauase we should not let the VM
modify the MAC. If
> > > > > we do it can set a MAC value identical to the mlx5 NIC
driver and can
> > > > > kidnap traffic that was not destined to it.
> > > > >
> > > > > In addition, when VIRTIO_NET_F_MAC is published,
attempts to change the
> > > > > MAC address from the VM should result in error.
> > > > That is not what the spec says though.
> > > > VIRTIO_NET_F_MAC only says whether mac is valid in the
config space.
> > > > Whether guest can control that depends on
VIRTIO_NET_F_CTRL_MAC_ADDR:
> > > >
> > > > 	The VIRTIO_NET_CTRL_MAC_ADDR_SET command is used to set the
default MAC address which rx
> > > > 	filtering accepts (and if VIRTIO_NET_F_MAC_ADDR has been
negotiated, this will be reflected in mac in
> > > > 	config space).
> > > > 	The command-specific-data for VIRTIO_NET_CTRL_MAC_ADDR_SET
is the 6-byte MAC address.
> > >
> > >
> > > Consider VIRTIO_NET_CTRL_MAC_ADDR_SET is not supported now. What
Eli
> > > proposed here should work?
> > >
> > > Thanks
> > >
> >
> > We can have management set a MAC address. Randomizing it in kernel
> > does not seem like a reasonable policy to me ...
> >
>
> This manangement should be the VDPA tool that Parav is pushing. We can
> use it to set a MAC chosen by the user. The mlx5 vdpa driver can then
> use that MAC instead of randomizing a value. If no admin value is given
> we can use a random MAC.

IIUC in this model devices are created by this tool, right?
Why not require the MAC when device is created?

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