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[91.219.240.17]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3db9b973869sm22277715f8f.18.2025.09.08.02.05.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Sep 2025 02:05:48 -0700 (PDT) From: Vitaly Kuznetsov To: Khushit Shah Cc: "seanjc@google.com" , "pbonzini@redhat.com" ,"kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Shaju Abraham Subject: Re: [BUG] [KVM/VMX] Level triggered interrupts mishandled on Windows w/ nested virt(Credential Guard) when using split irqchip In-Reply-To: <7D497EF1-607D-4D37-98E7-DAF95F099342@nutanix.com> References: <7D497EF1-607D-4D37-98E7-DAF95F099342@nutanix.com> Date: Mon, 08 Sep 2025 12:05:47 +0300 Message-ID: <87a535fh5g.fsf@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Khushit Shah writes: [trimmed 'Cc' list a bit] > [1.] One line summary: > [KVM/VMX] Level triggered interrupts mishandled on Windows w/ nested virt(Credential Guard) when using split irqchip > > [2.] Problem/Report: > When running Windows with Credential Guard enabled and with split-irqchip, level triggered interrupts are not properly forwarded to L2 (Credential Guard) by L1 (Windows), instead L1 EOIs the interrupt. Which leads to extremely slow Windows boot time. This issue is only seen on Intel + split-irqchip. Intel + kernel-irqchip, AMD + (kernel/split)-irqchip works fine. > > Qemu command used to create the vm: > /usr/libexec/qemu-kvm \ > -machine q35,accel=kvm,smm=on,usb=off,acpi=on,kernel-irqchip=split \ > -cpu host,+vmx,+invpcid,+ssse3,+aes,+xsave,+xsaveopt,+xgetbv1,+xsaves,+rdtscp,+tsc-deadline \ 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. > -m 20G -smp 1 \ Single CPU Windows guests are always very slow, doubly so when running nested. ... -- Vitaly