On Fri, Jun 01, 2018 at 10:22:59AM -0700, Samudrala, Sridhar wrote: > > > On 6/1/2018 8:48 AM, Michael S. Tsirkin wrote: > > On Fri, Jun 01, 2018 at 08:26:03AM -0700, Samudrala, Sridhar wrote: > > > On 5/31/2018 6:28 PM, Venu Busireddy wrote: > > > > I looked at the discussion in the threads [1] and [2], where it was > > > > suggested placing the passthrough device behind one bridge, and the > > > > virtio > > > > device behind another bridge, and storing in those bridges' > > > > configuration > > > > space some unique identifier that can be used to pair the two devices. > > > > > > > > After some discussions with Si-Wei Liu and others, we believe that the > > > > following scheme may be a viable approach. Please take a look at this > > > > proposal and provide your thoughts. > > > > > > > > 1. Enhance the QEMU CLI to include a "group_id" option to the bridge > > > > devices for Q35 as well as i440FX models. I have already made > > > > changes > > > > for the Q35 model (ioh3420 bridge). > > > > > > > > 2. When the guest is created, the operator creates two bridge devices > > > > (for example, using '-device ioh3420,group_id="string"'), and > > > > specifies > > > > a unique identifier string for both bridges. This identifier can be > > > > the UUID generated by 'uuidgen' command. > > > > > > > > 3. QEMU places this unique identifier in the PCI configuration space of > > > > the bridge as Vendor-Specific capability (0x09). The "Vendor" here > > > > is > > > > not to be confused with a specific organization. Instead, the > > > > vendor > > > > of the bridge is QEMU (with vendor ID 0x8086 and device ID 0x3420). > > > > > > > > 4. The operator places the passthrough device behind one of the bridges, > > > > and the virtio device behind the other bridge. > > > > > > > > 5. Patch 4 in patch series [3] should be modified to use the unique > > > > identifier string stored in the bridges' configuration space > > > > instead > > > > of the MAC address for pairing the devices. > > > This should be an alternate option that allows failover slaves to be > > > registered > > > based on MAC and ID. > > I wonder whether we ever want to pair based solely on ID and not on MAC. > > There used to be devices which randomized VF MAC on each reset but I > > think most of them have been changed to get MAC from the PF. Not sure > > whether any are left. > > Yes. I also don't think we need to support pairing based solely on ID. It > has be based > on MAC OR MAC+ID combination. > > > > > If we want the flexibility, we can use a separate feature bit for > > matching by ID. If not we can just extend the meaning of the > > existing one. > > Sure. If we can use 0 ID as MAC based pairing, it may be possible to extend > this without any new feature bit.
Not sure what does 0 ID mean. If it's in a capability, you just don't add the capability. > > > > > > > If it is desirable to create only one bridge instead of two (to conserve > > > > the number of devices in the system), then the passthrough device can > > > > be > > > > attached to that single bridge (with the identifier), and the identifier > > > > for the virtio device can be stored in the virtio device's configuration > > > > space itself. To do that, we need to update the virtio specification, > > > > and I have sent a proposal [4] to the OASIS team to update the virtio > > > > specification. If that proposal is accepted, then we can modify QEMU to > > > > use the virtio device's configuration space instead of the second bridge > > > > to store the unique identifier. > > > I think one bridge solution is much cleaner than having to use 2 bridges. > > > > > So for one bridge, we'd have a bridge with a special device/vendor ID, > > if virtio is behind that, we use that for pairing. > > > > > > > > Thank you for sparing the time. > > > > > > > > Venu > > > > > > > > [1] https://www.spinics.net/lists/linux-virtualization/msg33518.html > > > > [2] https://www.spinics.net/lists/netdev/msg499011.html > > > > [3] https://patchwork.ozlabs.org/cover/920005/ > > > > [4] > > > > https://lists.oasis-open.org/archives/virtio-dev/201805/msg00118.html > > > > > > > > > > > > --------------------------------------------------------------------- > > > > To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org > > > > For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org > > For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
