From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48780C433DB for ; Mon, 29 Mar 2021 14:51:57 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D588861964 for ; Mon, 29 Mar 2021 14:51:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D588861964 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46606 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lQtFE-0004CB-1D for qemu-devel@archiver.kernel.org; Mon, 29 Mar 2021 10:51:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44602) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lQtCu-00030y-GC for qemu-devel@nongnu.org; Mon, 29 Mar 2021 10:49:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:28045) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lQtCp-0002yS-QE for qemu-devel@nongnu.org; Mon, 29 Mar 2021 10:49:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617029366; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=mPOxFs9jHTEG/2pU3P/BqdEJcn3SM758fByuuvtdLrQ=; b=IKtB/sqTcz/tOJXPQ1sUdFgjg/0iVnhQ8CSFeickHUH8nvpfqAWUkwcTc7n6J6Xapq1qSD fH1T8fglMz56PEm43KZYDvHctk2QKzUK+u0TPaKMdKV5B2ig7Q8FakdYPo4sygXb7r48PQ r+WdRq3j0RF9j98p3695sAOcIr0XpJI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-505-b9sEbFWvNxuZtyW81djcXA-1; Mon, 29 Mar 2021 10:49:24 -0400 X-MC-Unique: b9sEbFWvNxuZtyW81djcXA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 23890108BD0D; Mon, 29 Mar 2021 14:49:23 +0000 (UTC) Received: from work-vm (ovpn-114-160.ams2.redhat.com [10.36.114.160]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A855B10016FD; Mon, 29 Mar 2021 14:49:15 +0000 (UTC) Date: Mon, 29 Mar 2021 15:49:13 +0100 From: "Dr. David Alan Gilbert" To: Vitaly Kuznetsov Subject: Re: [PATCH v2] i386: Make migration fail when Hyper-V reenlightenment was enabled but 'user_tsc_khz' is unset Message-ID: References: <20210319123801.1111090-1-vkuznets@redhat.com> <87y2e69lg8.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 In-Reply-To: <87y2e69lg8.fsf@vitty.brq.redhat.com> User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Marcelo Tosatti , Richard Henderson , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Vitaly Kuznetsov (vkuznets@redhat.com) wrote: > "Dr. David Alan Gilbert" writes: > > > * Vitaly Kuznetsov (vkuznets@redhat.com) wrote: > >> KVM doesn't fully support Hyper-V reenlightenment notifications on > >> migration. In particular, it doesn't support emulating TSC frequency > >> of the source host by trapping all TSC accesses so unless TSC scaling > >> is supported on the destination host and KVM_SET_TSC_KHZ succeeds, it > >> is unsafe to proceed with migration. > >> > >> KVM_SET_TSC_KHZ is called from two sites: kvm_arch_init_vcpu() and > >> kvm_arch_put_registers(). The later (intentionally) doesn't propagate > >> errors allowing migrations to succeed even when TSC scaling is not > >> supported on the destination. This doesn't suit 're-enlightenment' > >> use-case as we have to guarantee that TSC frequency stays constant. > >> > >> Require 'tsc-frequency=' command line option to be specified for successful > >> migration when re-enlightenment was enabled by the guest. > >> > >> Signed-off-by: Vitaly Kuznetsov > >> --- > >> This patch is a successor of "[PATCH 3/3] i386: Make sure > >> kvm_arch_set_tsc_khz() succeeds on migration when 'hv-reenlightenment' > >> was exposed" taking a different approach suggested by Paolo. > >> --- > >> docs/hyperv.txt | 5 +++++ > >> target/i386/kvm/hyperv-proto.h | 1 + > >> target/i386/machine.c | 20 ++++++++++++++++++++ > >> 3 files changed, 26 insertions(+) > >> > >> diff --git a/docs/hyperv.txt b/docs/hyperv.txt > >> index 5df00da54fc4..e53c581f4586 100644 > >> --- a/docs/hyperv.txt > >> +++ b/docs/hyperv.txt > >> @@ -160,6 +160,11 @@ the hypervisor) until it is ready to switch to the new one. This, in conjunction > >> with hv-frequencies, allows Hyper-V on KVM to pass stable clocksource (Reference > >> TSC page) to its own guests. > >> > >> +Note, KVM doesn't fully support re-enlightenment notifications and doesn't > >> +emulate TSC accesses after migration so 'tsc-frequency=' CPU option also has to > >> +be specified to make migration succeed. The destination host has to either have > >> +the same TSC frequency or support TSC scaling CPU feature. > >> + > >> Recommended: hv-frequencies > >> > >> 3.16. hv-evmcs > >> diff --git a/target/i386/kvm/hyperv-proto.h b/target/i386/kvm/hyperv-proto.h > >> index 056a305be38c..e30d64b4ade4 100644 > >> --- a/target/i386/kvm/hyperv-proto.h > >> +++ b/target/i386/kvm/hyperv-proto.h > >> @@ -139,6 +139,7 @@ > >> * Reenlightenment notification MSRs > >> */ > >> #define HV_X64_MSR_REENLIGHTENMENT_CONTROL 0x40000106 > >> +#define HV_REENLIGHTENMENT_ENABLE_BIT (1u << 16) > >> #define HV_X64_MSR_TSC_EMULATION_CONTROL 0x40000107 > >> #define HV_X64_MSR_TSC_EMULATION_STATUS 0x40000108 > >> > >> diff --git a/target/i386/machine.c b/target/i386/machine.c > >> index 7259fe6868c6..137604ddb898 100644 > >> --- a/target/i386/machine.c > >> +++ b/target/i386/machine.c > >> @@ -883,11 +883,31 @@ static bool hyperv_reenlightenment_enable_needed(void *opaque) > >> env->msr_hv_tsc_emulation_status != 0; > >> } > >> > >> +static int hyperv_reenlightenment_post_load(void *opaque, int version_id) > >> +{ > >> + X86CPU *cpu = opaque; > >> + CPUX86State *env = &cpu->env; > >> + > >> + /* > >> + * KVM doesn't fully support re-enlightenment notifications so we need to > >> + * make sure TSC frequency doesn't change upon migration. > >> + */ > >> + if ((env->msr_hv_reenlightenment_control & HV_REENLIGHTENMENT_ENABLE_BIT) && > >> + !env->user_tsc_khz) { > >> + error_report("Guest enabled re-enlightenment notifications, " > >> + "'tsc-frequency=' has to be specified"); > > > > It's unusual to fail on the destination for a valid configuration but > > guest state; wouldn't it be better to always insist on tsc-frequency if > > that hv feature is exposed; failing early before reeiving the state? > > > > Doing so would make a number of currently existing configurations > invalid, even when re-enlightenment is not to be used by the > guest. AFAIR Windows without Hyper-V doesn't enable it. Generally, we > just advise people to 'enable all currently supported hyper-v > enlightenments' to make things easier so reenlightenment may end up > being added for no particular reason. Ouch, that's difficult - the problem with testing this late is that the migration fails right at the end so it's an unpleasent surprise. Could you disallow re-enlightenment without tsc-frequency on new machine types? Dave > FWIW, v1 of this patch used a slightly different approach: I was > requiring kvm_arch_set_tsc_khz() to succeed. This is not exactly the > same as e.g. even when the destination host doesn't support TSC scaling, > it may happen to have the same TSC frequency. > > -- > Vitaly > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK