> On 11. Feb 2026, at 16:08, Peter Maydell <[email protected]> wrote:
>
> On Wed, 11 Feb 2026 at 12:50, Mohamed Mediouni <[email protected]>
> wrote:
>>
>>
>>
>>> On 11. Feb 2026, at 13:27, Mohammadfaiz Bawa <[email protected]> wrote:
>>>
>>> Windows ARM64 guests detect virtio-mmio devices declared in ACPI
>>> tables even when no backend is attached. This causes "Unknown
>>> devices" (ACPI\LNRO0005) to appear in Device Manager.
>
> Is that a problem? There's a device there, and Windows doesn't
> support it, so it reports that there's a device there that
> it doesn't support, which seems reasonable enough.
>
Hello,
For customers, some security software gets quite unhappy if it sees
that there are devices with no drivers installed.
For development it indeed doesn’t matter.
>>>
>>> Until Windows fixes that by supporting, adding a new machine
>>> property 'virtio-transports' to control the number of
>>> virtio-mmio transports instantiated. The default remains
>>> NUM_VIRTIO_TRANSPORTS (32) for backward compatibility.
>>> Setting it to 0 allows users to disable virtio-mmio entirely.
>>>
>>> Usage: -machine virt,virtio-transports=0
>>
>> Hello,
>>
>> With keeping in mind that this was documented in this (closed…) issue
>> https://github.com/virtio-win/kvm-guest-drivers-windows/issues/595
>>
>> Reviewed-by: Mohamed Mediouni <[email protected]>
>
>>> + if (transports > NUM_VIRTIO_TRANSPORTS) {
>>> + error_setg(errp, "virtio-transports must not exceed %d",
>>> + NUM_VIRTIO_TRANSPORTS);
>> Any particular reason to (keep) capping the maximum to 16?
>>
>> From a cursory look, base_memmap seems to have room for plenty more.
>
> My first question to anybody wanting more than 32 here would be
> "why are you not using virtio-pci" ? The whole virtio-mmio infra
> in the virt board is only here because at the time we had no PCI
> support.
>
Could it make sense to have it disabled by default for new machine model
versions then?
Thank you,
-Mohamed
> The advantage of this series to me is that it means we have
> a way for users to say "I'm not using this functionality,
> just turn it off completely" which lets them reduce the
> security surface a little.
>
> The other thing worth checking is whether we're correctly
> following the ACPI spec in exposing virtio-transports with
> nothing plugged into them, or if we're supposed to be
> suppressing them.
>
> thanks
> -- PMM
