Re: [PATCH v2 1/1] hw/s390x/ccw: Disable legacy virtio-pci by default (v11.1+)

[Halil Pasic <pasic@linux.ibm.com>]

On Mon, 20 Apr 2026 09:47:34 -0500
Jaehoon Kim <jhkim@linux.ibm.com> wrote:

> On the s390 Linux kernel, IO_SPACE_LIMIT has been 0 since the initial
> zPCI implementation (commit cd24834130ac "s390/pci: base support"),
> making I/O BARs unusable.
> 
> However, when virtio-pci devices operate in transitional mode, QEMU
> unconditionally exposes the legacy interface via BAR0. This results in
> firmware warnings during PCI enumeration, such as:
> 
>   pci 0005:00:00.0: [Firmware Bug]: BAR 0: invalid; can't size
> 
> even though BAR0 is never usable on the s390 kernel.
> 
> Close this gap by disabling legacy virtio-pci support starting from
> machine version 11.1. This effectively makes virtio-pci devices
> non-transitional and prevents the creation of the unusable legacy I/O
> BAR.
> 
> This introduces s390x-specific global compatibility properties that
> set disable-legacy=on as the default for virtio-pci devices. Machine
> versions v11.0 and earlier set disable-legacy=off to maintain their
> original default behavior (legacy support enabled), ensuring VMs
> created with those versions continue to work identically.
> 
> Users can override the default on the command line if needed:
>   - On v11.1+: -global virtio-pci.disable-legacy=off (to enable legacy)
>   - On v11.0-: -global virtio-pci.disable-legacy=on (to disable legacy)
> 
> Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>
> Reviewed-by: Mohamed Mediouni <mohamed@unpredictable.fr>

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>