Re: [BUG] [KVM/VMX] Level triggered interrupts mishandled on Windows w/ nested virt(Credential Guard) when using split irqchip

Khushit Shah
2025-09-08T11:20:14Z

Thanks you for the comments Vitaly!

> On 8 Sep 2025, at 2:35 PM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Is there a specific reason to not enable any Hyper-V enlightenments for
> your guest? For nested cases, features like Enightended VMCS
> ('hv-evmcs'), 'hv-vapic', 'hv-apicv', ... can change Windows's behavior
> a lot. I'd even suggest you start with 'hv-passthrough' to see if the
> slowness goes away and if yes, then try to find the required set of
> options you can use in your setup.

Actually in production we use an extensive set of cpu features exposed to the guest, still the issue persists,
With the following hv-* options also the issue is present:
hypervisor=on,hv-time=on,hv-relaxed=on,hv-vapic=on,hv-spinlocks=0x2000,hv-vpindex=on,hv-runtime=on,hv-synic=on,
hv-stimer=on,hv-tlbflush=on,hv-ipi=on,hv-evmcs=on

>
> On 8 Sep 2025, at 2:35 PM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Single CPU Windows guests are always very slow, doubly so when running nested.

The bug was reproducible even with more cpus like (4,8), we use 1 to reduce noise in captured logs.

I should also mention by slow boot we mean extremely slow (>3h).

Thanks,
Khushit