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Thu, 02 Dec 2021 05:21:13 -0500 X-MC-Unique: FTxu8o4JPGuzaC45aDiDWA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ABDFE81EE60; Thu, 2 Dec 2021 10:21:09 +0000 (UTC) Received: from starship (unknown [10.40.192.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id D73445D9CA; Thu, 2 Dec 2021 10:20:56 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful From: Maxim Levitsky To: Sean Christopherson Date: Thu, 02 Dec 2021 12:20:55 +0200 In-Reply-To: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mailman-Approved-At: Fri, 03 Dec 2021 08:46:41 -0500 Cc: Cornelia Huck , Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, Paul Mackerras , Atish Patra , linux-riscv@lists.infradead.org, Claudio Imbrenda , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , Albert Ou , kvm-ppc@vger.kernel.org, Paul Walmsley , David Matlack , linux-arm-kernel@lists.infradead.org, Jim Mattson , Anup Patel , linux-mips@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Paolo Bonzini , Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm