Linux Virtualization - Jun 2018 - [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

On Fri, Jun 22, 2018 at 3:25 PM, Michael S. Tsirkin <mst at redhat.com>
wrote:
> On Fri, Jun 22, 2018 at 02:51:11PM -0700, Siwei Liu wrote:
>> On Fri, Jun 22, 2018 at 2:29 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
>> > On Fri, Jun 22, 2018 at 01:03:04PM -0700, Siwei Liu wrote:
>> >> On Fri, Jun 22, 2018 at 1:00 PM, Siwei Liu <loseweigh at
gmail.com> wrote:
>> >> > On Thu, Jun 21, 2018 at 7:32 PM, Michael S. Tsirkin
<mst at redhat.com> wrote:
>> >> >> On Thu, Jun 21, 2018 at 06:21:55PM -0700, Siwei Liu
wrote:
>> >> >>> On Thu, Jun 21, 2018 at 7:59 AM, Cornelia Huck
<cohuck at redhat.com> wrote:
>> >> >>> > On Wed, 20 Jun 2018 22:48:58 +0300
>> >> >>> > "Michael S. Tsirkin" <mst at
redhat.com> wrote:
>> >> >>> >
>> >> >>> >> On Wed, Jun 20, 2018 at 06:06:19PM
+0200, Cornelia Huck wrote:
>> >> >>> >> > In any case, I'm not sure
anymore why we'd want the extra uuid.
>> >> >>> >>
>> >> >>> >> It's mostly so we can have e.g.
multiple devices with same MAC
>> >> >>> >> (which some people seem to want in order
to then use
>> >> >>> >> then with different containers).
>> >> >>> >>
>> >> >>> >> But it is also handy for when you assign
a PF, since then you
>> >> >>> >> can't set the MAC.
>> >> >>> >>
>> >> >>> >
>> >> >>> > OK, so what about the following:
>> >> >>> >
>> >> >>> > - introduce a new feature bit,
VIRTIO_NET_F_STANDBY_UUID that indicates
>> >> >>> >   that we have a new uuid field in the
virtio-net config space
>> >> >>> > - in QEMU, add a property for virtio-net
that allows to specify a uuid,
>> >> >>> >   offer VIRTIO_NET_F_STANDBY_UUID if set
>> >> >>> > - when configuring, set the property to the
group UUID of the vfio-pci
>> >> >>> >   device
>> >> >>>
>> >> >>> If feature negotiation fails on
VIRTIO_NET_F_STANDBY_UUID, is it safe
>> >> >>> to still expose UUID in the config space on
virtio-pci?
>> >> >>
>> >> >>
>> >> >> Yes but guest is not supposed to read it.
>> >> >>
>> >> >>> I'm not even sure if it's sane to expose
group UUID on the PCI bridge
>> >> >>> where the corresponding vfio-pci device attached
to for a guest which
>> >> >>> doesn't support the feature (legacy).
>> >> >>>
>> >> >>> -Siwei
>> >> >>
>> >> >> Yes but you won't add the primary behind such a
bridge.
>> >> >
>> >> > I assume the UUID feature is a new one besides the
exiting
>> >> > VIRTIO_NET_F_STANDBY feature, where I think the current
proposal is,
>> >> > if UUID feature is present and supported by guest,
we'll do pairing
>> >> > based on UUID; if UUID feature present
>> >>                                  ^^^^^^^  is NOT present
>> >
>> > Let's go back for a bit.
>> >
>> > What is wrong with matching by mac?
>> >
>> > 1. Does not allow multiple NICs with same mac
>> > 2. Requires MAC to be programmed by host in the PT device
>> >    (which is often possible with VFs but isn't possible with
all PT
>> >    devices)
>>
>> Might not neccessarily be something wrong, but it's very limited to
>> prohibit the MAC of VF from changing when enslaved by failover.
>
> You mean guest changing MAC? I'm not sure why we prohibit that.
I think Sridhar and Jiri might be better person to answer it. My
impression was that sync'ing the MAC address change between all 3
devices is challenging, as the failover driver uses MAC address to
match net_device internally.
>
>
>> The
>> same as you indicated on the PT device. I suspect the same is
>> prohibited on even virtio-net and failover is because of the same
>> limitation.
>>
>> >
>> > Both issues are up to host: if host needs them it needs the UUID
>> > feature, if not MAC matching is sufficient.
>>
>> I know. What I'm saying is that we rely on STANDBY feature to
control
>> the visibility of the primary, not the UUID feature.
>>
>> -Siwei
>
> And what I'm saying is that it's up to a host policy.
So lets say host policy explicitly requires UUID but the guest does
not support it. The guest could be a legacy guest with no STANDBY
support, or a relevately recent guest with STANDBY support but without
the UUID support. In either case, since host asked for UUID matching
explicitly, maybe because it requires different NIC using same MAC, so
it has to override the negotiation result of STANDBY, even if STANDBY
is set and supported? That will end up with inter-feature dependency
over STANDBY, as you see.

-Siwei
>
>> >
>> >
>> >> > or not supported by guest,
>> >> > we'll still plug in the VF (if guest supports the
_F_STANDBY feature)
>> >> > but the pairing will be fallback to using MAC address.
Are you saying
>> >> > you don't even want to plug in the primary when the
UUID feature is
>> >> > not supported by guest? Does the feature negotiation UUID
have to
>> >> > depend on STANDBY being set, or the other way around? I
thought that
>> >> > just the absence of STANDBY will prevent primary to get
exposed to the
>> >> > guest.
>> >> >
>> >> > -Siwei
>> >> >
>> >> >>
>> >> >>>
>> >> >>> > - in the guest, use the uuid from the
virtio-net device's config space
>> >> >>> >   if applicable; else, fall back to matching
by MAC as done today
>> >

On Fri, Jun 22, 2018 at 4:40 PM, Siwei Liu <loseweigh at gmail.com>
wrote:
> On Fri, Jun 22, 2018 at 3:25 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
>> On Fri, Jun 22, 2018 at 02:51:11PM -0700, Siwei Liu wrote:
>>> On Fri, Jun 22, 2018 at 2:29 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
>>> > On Fri, Jun 22, 2018 at 01:03:04PM -0700, Siwei Liu wrote:
>>> >> On Fri, Jun 22, 2018 at 1:00 PM, Siwei Liu <loseweigh
at gmail.com> wrote:
>>> >> > On Thu, Jun 21, 2018 at 7:32 PM, Michael S. Tsirkin
<mst at redhat.com> wrote:
>>> >> >> On Thu, Jun 21, 2018 at 06:21:55PM -0700, Siwei
Liu wrote:
>>> >> >>> On Thu, Jun 21, 2018 at 7:59 AM, Cornelia
Huck <cohuck at redhat.com> wrote:
>>> >> >>> > On Wed, 20 Jun 2018 22:48:58 +0300
>>> >> >>> > "Michael S. Tsirkin" <mst
at redhat.com> wrote:
>>> >> >>> >
>>> >> >>> >> On Wed, Jun 20, 2018 at 06:06:19PM
+0200, Cornelia Huck wrote:
>>> >> >>> >> > In any case, I'm not sure
anymore why we'd want the extra uuid.
>>> >> >>> >>
>>> >> >>> >> It's mostly so we can have e.g.
multiple devices with same MAC
>>> >> >>> >> (which some people seem to want in
order to then use
>>> >> >>> >> then with different containers).
>>> >> >>> >>
>>> >> >>> >> But it is also handy for when you
assign a PF, since then you
>>> >> >>> >> can't set the MAC.
>>> >> >>> >>
>>> >> >>> >
>>> >> >>> > OK, so what about the following:
>>> >> >>> >
>>> >> >>> > - introduce a new feature bit,
VIRTIO_NET_F_STANDBY_UUID that indicates
>>> >> >>> >   that we have a new uuid field in the
virtio-net config space
>>> >> >>> > - in QEMU, add a property for virtio-net
that allows to specify a uuid,
>>> >> >>> >   offer VIRTIO_NET_F_STANDBY_UUID if set
>>> >> >>> > - when configuring, set the property to
the group UUID of the vfio-pci
>>> >> >>> >   device
>>> >> >>>
>>> >> >>> If feature negotiation fails on
VIRTIO_NET_F_STANDBY_UUID, is it safe
>>> >> >>> to still expose UUID in the config space on
virtio-pci?
>>> >> >>
>>> >> >>
>>> >> >> Yes but guest is not supposed to read it.
>>> >> >>
>>> >> >>> I'm not even sure if it's sane to
expose group UUID on the PCI bridge
>>> >> >>> where the corresponding vfio-pci device
attached to for a guest which
>>> >> >>> doesn't support the feature (legacy).
>>> >> >>>
>>> >> >>> -Siwei
>>> >> >>
>>> >> >> Yes but you won't add the primary behind such
a bridge.
>>> >> >
>>> >> > I assume the UUID feature is a new one besides the
exiting
>>> >> > VIRTIO_NET_F_STANDBY feature, where I think the
current proposal is,
>>> >> > if UUID feature is present and supported by guest,
we'll do pairing
>>> >> > based on UUID; if UUID feature present
>>> >>                                  ^^^^^^^  is NOT present
>>> >
>>> > Let's go back for a bit.
>>> >
>>> > What is wrong with matching by mac?
>>> >
>>> > 1. Does not allow multiple NICs with same mac
>>> > 2. Requires MAC to be programmed by host in the PT device
>>> >    (which is often possible with VFs but isn't possible
with all PT
>>> >    devices)
>>>
>>> Might not neccessarily be something wrong, but it's very
limited to
>>> prohibit the MAC of VF from changing when enslaved by failover.
>>
>> You mean guest changing MAC? I'm not sure why we prohibit that.
>
> I think Sridhar and Jiri might be better person to answer it. My
> impression was that sync'ing the MAC address change between all 3
> devices is challenging, as the failover driver uses MAC address to
> match net_device internally.
>
>>
>>
>>> The
>>> same as you indicated on the PT device. I suspect the same is
>>> prohibited on even virtio-net and failover is because of the same
>>> limitation.
>>>
>>> >
>>> > Both issues are up to host: if host needs them it needs the
UUID
>>> > feature, if not MAC matching is sufficient.
>>>
>>> I know. What I'm saying is that we rely on STANDBY feature to
control
>>> the visibility of the primary, not the UUID feature.
>>>
>>> -Siwei
>>
>> And what I'm saying is that it's up to a host policy.
>
> So lets say host policy explicitly requires UUID but the guest does
> not support it. The guest could be a legacy guest with no STANDBY
> support, or a relevately recent guest with STANDBY support but without
> the UUID support. In either case, since host asked for UUID matching
> explicitly, maybe because it requires different NIC using same MAC, so
> it has to override the negotiation result of STANDBY, even if STANDBY
> is set and supported? That will end up with inter-feature dependency
> over STANDBY, as you see.
I forgot to mention the above has the assumption that we expose both
STANDBY and UUID feature to QEMU user. In fact, as we're going towards
not exposing the STANDBY feature directly to user, UUID may be always
required to enable STANDBY. If not, how do we make sure QEMU can
control the visibility of primary device? Something to be confirmed
before implementing the code.

-Siwei
>
> -Siwei
>
>>
>>> >
>>> >
>>> >> > or not supported by guest,
>>> >> > we'll still plug in the VF (if guest supports the
_F_STANDBY feature)
>>> >> > but the pairing will be fallback to using MAC
address. Are you saying
>>> >> > you don't even want to plug in the primary when
the UUID feature is
>>> >> > not supported by guest? Does the feature negotiation
UUID have to
>>> >> > depend on STANDBY being set, or the other way around?
I thought that
>>> >> > just the absence of STANDBY will prevent primary to
get exposed to the
>>> >> > guest.
>>> >> >
>>> >> > -Siwei
>>> >> >
>>> >> >>
>>> >> >>>
>>> >> >>> > - in the guest, use the uuid from the
virtio-net device's config space
>>> >> >>> >   if applicable; else, fall back to
matching by MAC as done today
>>> >

On Fri, Jun 22, 2018 at 05:17:10PM -0700, Siwei Liu
wrote:
> I forgot to mention the above has the assumption that we expose both
> STANDBY and UUID feature to QEMU user. In fact, as we're going towards
> not exposing the STANDBY feature directly to user, UUID may be always
> required to enable STANDBY.
Sounds good.
> If not, how do we make sure QEMU can
> control the visibility of primary device?
Hypervisors fundamentally always can control visibility of all
virtual devices.
> Something to be confirmed
> before implementing the code.
>

On 6/22/2018 5:17 PM, Siwei Liu wrote:
> On Fri, Jun 22, 2018 at 4:40 PM, Siwei Liu <loseweigh at gmail.com>
wrote:
>> On Fri, Jun 22, 2018 at 3:25 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
>>> On Fri, Jun 22, 2018 at 02:51:11PM -0700, Siwei Liu wrote:
>>>> On Fri, Jun 22, 2018 at 2:29 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
>>>>> On Fri, Jun 22, 2018 at 01:03:04PM -0700, Siwei Liu wrote:
>>>>>> On Fri, Jun 22, 2018 at 1:00 PM, Siwei Liu
<loseweigh at gmail.com> wrote:
>>>>>>> On Thu, Jun 21, 2018 at 7:32 PM, Michael S. Tsirkin
<mst at redhat.com> wrote:
>>>>>>>> On Thu, Jun 21, 2018 at 06:21:55PM -0700, Siwei
Liu wrote:
>>>>>>>>> On Thu, Jun 21, 2018 at 7:59 AM, Cornelia
Huck <cohuck at redhat.com> wrote:
>>>>>>>>>> On Wed, 20 Jun 2018 22:48:58 +0300
>>>>>>>>>> "Michael S. Tsirkin" <mst
at redhat.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> On Wed, Jun 20, 2018 at 06:06:19PM
+0200, Cornelia Huck wrote:
>>>>>>>>>>>> In any case, I'm not sure
anymore why we'd want the extra uuid.
>>>>>>>>>>> It's mostly so we can have e.g.
multiple devices with same MAC
>>>>>>>>>>> (which some people seem to want in
order to then use
>>>>>>>>>>> then with different containers).
>>>>>>>>>>>
>>>>>>>>>>> But it is also handy for when you
assign a PF, since then you
>>>>>>>>>>> can't set the MAC.
>>>>>>>>>>>
>>>>>>>>>> OK, so what about the following:
>>>>>>>>>>
>>>>>>>>>> - introduce a new feature bit,
VIRTIO_NET_F_STANDBY_UUID that indicates
>>>>>>>>>>    that we have a new uuid field in the
virtio-net config space
>>>>>>>>>> - in QEMU, add a property for
virtio-net that allows to specify a uuid,
>>>>>>>>>>    offer VIRTIO_NET_F_STANDBY_UUID if
set
>>>>>>>>>> - when configuring, set the property to
the group UUID of the vfio-pci
>>>>>>>>>>    device
>>>>>>>>> If feature negotiation fails on
VIRTIO_NET_F_STANDBY_UUID, is it safe
>>>>>>>>> to still expose UUID in the config space on
virtio-pci?
>>>>>>>>
>>>>>>>> Yes but guest is not supposed to read it.
>>>>>>>>
>>>>>>>>> I'm not even sure if it's sane to
expose group UUID on the PCI bridge
>>>>>>>>> where the corresponding vfio-pci device
attached to for a guest which
>>>>>>>>> doesn't support the feature (legacy).
>>>>>>>>>
>>>>>>>>> -Siwei
>>>>>>>> Yes but you won't add the primary behind
such a bridge.
>>>>>>> I assume the UUID feature is a new one besides the
exiting
>>>>>>> VIRTIO_NET_F_STANDBY feature, where I think the
current proposal is,
>>>>>>> if UUID feature is present and supported by guest,
we'll do pairing
>>>>>>> based on UUID; if UUID feature present
>>>>>>                                   ^^^^^^^  is NOT
present
>>>>> Let's go back for a bit.
>>>>>
>>>>> What is wrong with matching by mac?
>>>>>
>>>>> 1. Does not allow multiple NICs with same mac
>>>>> 2. Requires MAC to be programmed by host in the PT device
>>>>>     (which is often possible with VFs but isn't
possible with all PT
>>>>>     devices)
>>>> Might not neccessarily be something wrong, but it's very
limited to
>>>> prohibit the MAC of VF from changing when enslaved by failover.
>>> You mean guest changing MAC? I'm not sure why we prohibit that.
>> I think Sridhar and Jiri might be better person to answer it. My
>> impression was that sync'ing the MAC address change between all 3
>> devices is challenging, as the failover driver uses MAC address to
>> match net_device internally.
Yes. The MAC address is assigned by the hypervisor and it needs to manage the
movement
of the MAC between the PF and VF.? Allowing the guest to change the MAC will
require
synchronization between the hypervisor and the PF/VF drivers. Most of the VF
drivers
don't allow changing guest MAC unless it is a trusted VF.