Re: [PULL 04/17] virtio-net: Add support for USO features

[Fiona Ebner <f.ebner@proxmox.com>]

Hi,

Am 08.09.23 um 08:44 schrieb Jason Wang:
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index da699cf..230aab8 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -38,6 +38,7 @@
>  #include "exec/confidential-guest-support.h"
>  #include "hw/virtio/virtio.h"
>  #include "hw/virtio/virtio-pci.h"
> +#include "hw/virtio/virtio-net.h"
>  
>  GlobalProperty hw_compat_8_1[] = {};
>  const size_t hw_compat_8_1_len = G_N_ELEMENTS(hw_compat_8_1);
> @@ -45,6 +46,9 @@ const size_t hw_compat_8_1_len = G_N_ELEMENTS(hw_compat_8_1);
>  GlobalProperty hw_compat_8_0[] = {
>      { "migration", "multifd-flush-after-each-section", "on"},
>      { TYPE_PCI_DEVICE, "x-pcie-ari-nextfn-1", "on" },
> +    { TYPE_VIRTIO_NET, "host_uso", "off"},
> +    { TYPE_VIRTIO_NET, "guest_uso4", "off"},
> +    { TYPE_VIRTIO_NET, "guest_uso6", "off"},
>  };
>  const size_t hw_compat_8_0_len = G_N_ELEMENTS(hw_compat_8_0);
>  

unfortunately, this broke backwards migration with machine version 8.1
from 8.2 and 9.0 binaries to a 8.1 binary:

> kvm: Features 0x1c0010130afffa7 unsupported. Allowed features: 0x10179bfffe7
> kvm: Failed to load virtio-net:virtio
> kvm: error while loading state for instance 0x0 of device '0000:00:12.0/virtio-net'
> kvm: load of migration failed: Operation not permitted

Since the series here only landed in 8.2, shouldn't these flags have
been added to hw_compat_8_1[] instead?

Attempting to fix it by moving the flags will break migration with
machine version 8.1 between patched 9.0 and unpatched 9.0 however :(

Is there anything that can be done or will it need to stay broken now?

CC-ing the migration maintainers.

Best Regards,
Fiona