On Tue, Sep 07, 2021 at 02:49:35PM +0200, Stefano Garzarella wrote:
> Commit 1e08fd0a46 ("vhost-vsock: SOCK_SEQPACKET feature bit support")
> enabled the SEQPACKET feature bit.
> This commit is released with QEMU 6.1, so if we try to migrate a VM where
> the host kernel supports SEQPACKET but machine type version is less than
> 6.1, we get the following errors:
>
> Features 0x130000002 unsupported. Allowed features: 0x179000000
> Failed to load virtio-vhost_vsock:virtio
> error while loading state for instance 0x0 of device
> '0000:00:05.0/virtio-vhost_vsock'
> load of migration failed: Operation not permitted
>
> Let's disable the feature bit for machine types < 6.1, adding a
> `features` field to VHostVSock to simplify the handling of upcoming
> features we will support.
IIUC, this will still leave migration broken for anyone migrating
a >= 6.1 machine type between a kernel that supports SEQPACKET and
a kernel lacking that, or vica-verca.
If a feature is dependant on a host kernel feature we can't turn
that on automatically as part of the machine type, as we need
ABI stability across migration indepdant of kernel version.
Regards,
Daniel
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