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[91.219.240.17]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e705508e22sm8404675f8f.49.2025.09.08.04.42.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Sep 2025 04:42:30 -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: References: <7D497EF1-607D-4D37-98E7-DAF95F099342@nutanix.com> <87a535fh5g.fsf@redhat.com> Date: Mon, 08 Sep 2025 14:42:29 +0300 Message-ID: <87wm69dvbu.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Khushit Shah writes: > Thanks you for the comments Vitaly! > >> On 8 Sep 2025, at 2:35 PM, Vitaly Kuznetsov 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 > Try adding 'hv-apicv' (AKA 'hv-avic') to the list too (not to be confused with 'hv-vapic'). >> >> On 8 Sep 2025, at 2:35 PM, Vitaly Kuznetsov 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). Oh, this is next level) Do you know if the issue reproduces with newer Windows, e.g. 2025? Also, I've just recalled I fixed (well, 'workarounded') an issue similar to yours a while ago in QEMU: commit 958a01dab8e02fc49f4fd619fad8c82a1108afdb Author: Vitaly Kuznetsov Date: Tue Apr 2 10:02:15 2019 +0200 ioapic: allow buggy guests mishandling level-triggered interrupts to make progress maybe something has changed and it doesn't work anymore? -- Vitaly