Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 37A0EC61DA4 for ; Thu, 16 Feb 2023 14:40:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230100AbjBPOk1 (ORCPT ); Thu, 16 Feb 2023 09:40:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229512AbjBPOkX (ORCPT ); Thu, 16 Feb 2023 09:40:23 -0500 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 0426F4486; Thu, 16 Feb 2023 06:40:23 -0800 (PST) Received: from [192.168.2.24] (77-166-152-30.fixed.kpn.net [77.166.152.30]) by linux.microsoft.com (Postfix) with ESMTPSA id 55278203B3ED; Thu, 16 Feb 2023 06:40:21 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 55278203B3ED DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1676558422; bh=sJG+NSOBI5mC5iqs3AMRqDZX2NzuSVuPzCVOQDWiLK8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PbVQxtzEMrllbRz5ywLWWdzp//0mLx7fEWiTa6K+uDSPx6yzIm7Ik2b4608Eb/uOM 2iuhH6JkahCxpzLOfPhSD5Z5JnrGH6tI1B7fId8DHuorkRXF2YIppJPbrBgS26qpzq INhlL76BvWiVFUzTvGj+28sSi6doxoPWU4bvuSB8= Message-ID: <7e1d3590-2205-401c-c6f5-e4da534d85a7@linux.microsoft.com> Date: Thu, 16 Feb 2023 15:40:20 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: "KVM: x86/mmu: Overhaul TDP MMU zapping and flushing" breaks SVM on Hyper-V Content-Language: en-US To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Tianyu Lan , "Michael Kelley (LINUX)" References: <43980946-7bbf-dcef-7e40-af904c456250@linux.microsoft.com> <35ff8f48-2677-78ea-b5f3-329c75ce65c9@redhat.com> <20d189fc-8d20-8083-b448-460cc0420151@linux.microsoft.com> From: Jeremi Piotrowski In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/02/2023 23:16, Sean Christopherson wrote: > On Tue, Feb 14, 2023, Jeremi Piotrowski wrote: >> On 13/02/2023 20:56, Paolo Bonzini wrote: >>> On Mon, Feb 13, 2023 at 8:12 PM Sean Christopherson wrote: >>>>> Depending on the performance results of adding the hypercall to >>>>> svm_flush_tlb_current, the fix could indeed be to just disable usage of >>>>> HV_X64_NESTED_ENLIGHTENED_TLB. >>>> >>>> Minus making nested SVM (L3) mutually exclusive, I believe this will do the trick: >>>> >>>> + /* blah blah blah */ >>>> + hv_flush_tlb_current(vcpu); >>>> + >>> >>> Yes, it's either this or disabling the feature. >>> >>> Paolo >> >> Combining the two sub-threads: both of the suggestions: >> >> a) adding a hyperv_flush_guest_mapping(__pa(root->spt) after kvm_tdp_mmu_get_vcpu_root_hpa's call to tdp_mmu_alloc_sp() >> b) adding a hyperv_flush_guest_mapping(vcpu->arch.mmu->root.hpa) to svm_flush_tlb_current() >> >> appear to work in my test case (L2 vm startup until panic due to missing rootfs). >> >> But in both these cases (and also when I completely disable HV_X64_NESTED_ENLIGHTENED_TLB) >> the runtime of an iteration of the test is noticeably longer compared to tdp_mmu=0. > > Hmm, what is test doing? Booting through OVMF and kernel with no rootfs provided, and panic=-1 specified on the kernel command line. It's a pure startup time test. > >> So in terms of performance the ranking is (fastest to slowest): >> 1. tdp_mmu=0 + enlightened TLB >> 2. tdp_mmu=0 + no enlightened TLB >> 3. tdp_mmu=1 (enlightened TLB makes minimal difference)