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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]:42254 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kIy0r-0003Wl-Nf for qemu-devel@archiver.kernel.org; Thu, 17 Sep 2020 13:48:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44426) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kIxxQ-0000uF-RZ for qemu-devel@nongnu.org; Thu, 17 Sep 2020 13:44:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:40136) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kIxxP-00037y-2O for qemu-devel@nongnu.org; Thu, 17 Sep 2020 13:44:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600364670; 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=/yqIInjnTal9RXjvDBvExWKgy52J0VRy7RBX+TE8S7A=; b=aCQYz62Zs7fbRqQXa57ekZXlDcPXSIkDeXqxI6CQeEkW1J094o5Z8a6qgsCo5lWWC8Uc4y 6hHwxH0mipQU8E1ymgEyYoVqT+Ga6RIlsBWgNT52+8m+VrLiEyi/MY1fHQJ8G/hh9G4Pi5 Ks/2ev5Ib9FC3PO+7vCnv/KJRUElW/g= 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-281-A0C3sWcCNFudyKkEB7s4vw-1; Thu, 17 Sep 2020 13:44:27 -0400 X-MC-Unique: A0C3sWcCNFudyKkEB7s4vw-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 4B2E9100CAB8; Thu, 17 Sep 2020 17:44:26 +0000 (UTC) Received: from work-vm (ovpn-114-108.ams2.redhat.com [10.36.114.108]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 11C5560C57; Thu, 17 Sep 2020 17:44:12 +0000 (UTC) Date: Thu, 17 Sep 2020 18:44:10 +0100 From: "Dr. David Alan Gilbert" To: Vitaly Kuznetsov Subject: Re: [PATCH] target/i386: always create kvmclock device Message-ID: <20200917174410.GU2793@work-vm> References: <20200917111306.819263-1-vkuznets@redhat.com> <20200917122559.e7i5o64k7rw7urdh@tartarus> <87ft7gh6gy.fsf@vitty.brq.redhat.com> <20200917144237.GK2793@work-vm> <875z8ch2m6.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 In-Reply-To: <875z8ch2m6.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/17 02:01:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.997, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=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: Antoine Damhet , Paolo Bonzini , Marcelo Tosatti , 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: > >> Antoine Damhet writes: > >> > >> > On Thu, Sep 17, 2020 at 01:13:06PM +0200, Vitaly Kuznetsov wrote: > >> >> QEMU's kvmclock device is only created when KVM PV feature bits for > >> >> kvmclock (KVM_FEATURE_CLOCKSOURCE/KVM_FEATURE_CLOCKSOURCE2) are > >> >> exposed to the guest. With 'kvm=off' cpu flag the device is not > >> >> created and we don't call KVM_GET_CLOCK/KVM_SET_CLOCK upon migration. > >> >> It was reported that without these call at least Hyper-V TSC page > >> >> clocksouce (which can be enabled independently) gets broken after > >> >> migration. > >> >> > >> >> Switch to creating kvmclock QEMU device unconditionally, it seems > >> >> to always make sense to call KVM_GET_CLOCK/KVM_SET_CLOCK on migration. > >> >> Use KVM_CAP_ADJUST_CLOCK check instead of CPUID feature bits. > >> >> > >> >> Reported-by: Antoine Damhet > >> >> Suggested-by: Paolo Bonzini > >> >> Signed-off-by: Vitaly Kuznetsov > >> >> --- > >> >> hw/i386/kvm/clock.c | 6 +----- > >> >> target/i386/kvm.c | 5 +++++ > >> >> target/i386/kvm_i386.h | 1 + > >> >> 3 files changed, 7 insertions(+), 5 deletions(-) > >> >> > >> >> diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c > >> >> index 64283358f91d..526c9ea5172b 100644 > >> >> --- a/hw/i386/kvm/clock.c > >> >> +++ b/hw/i386/kvm/clock.c > >> >> @@ -330,11 +330,7 @@ static const TypeInfo kvmclock_info = { > >> >> /* Note: Must be called after VCPU initialization. */ > >> >> void kvmclock_create(void) > >> >> { > >> >> - X86CPU *cpu = X86_CPU(first_cpu); > >> >> - > >> >> - if (kvm_enabled() && > >> >> - cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) | > >> >> - (1ULL << KVM_FEATURE_CLOCKSOURCE2))) { > >> >> + if (kvm_enabled() && kvm_has_adjust_clock()) { > >> > > >> > Shouldn't the old check used when machine type <= 5.1 in order to avoid > >> > migration incompatibility ? > >> > >> Hm, when the check fails we just don't create the device and no error is > >> reported, so even if we have kvmclock data in the migration stream but > >> fail to create it migration will still succeed, right? (not a migration > >> expert here :-) > > > > When the migration stream is parsed, it'll try and find a "kvmclock" > > device to pass the data it's reading to; if one doesn't exist it'll > > fail. > > This may happen with an older machine type when the destination is > running an unfixed QEMU and the source has the fix, right? Yes I think so. > The solution > would be to introduce a flag for older machine types (or for new ones) > like 'kvmclock_always'. Yep sounds the normal answer. (You might want to try it first to trigger the bug) > > The other question is in the incoming direction from an older VM; > > you'll have a kvm clock created here, but you won't load the kvm clock > > state from the migration stream - what is this clock going to do? > > This is not really a problem I believe: the clock was absent on the > source and things somehow worked for the guest so even if we don't > initialize kvmclock properly on the destination nothing bad is expected. OK. Dave > > > > Dave > > > >> > > >> >> sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL); > >> >> } > >> >> } > >> >> diff --git a/target/i386/kvm.c b/target/i386/kvm.c > >> >> index 4a8b3a41c1bc..20b31b65307b 100644 > >> >> --- a/target/i386/kvm.c > >> >> +++ b/target/i386/kvm.c > >> >> @@ -143,6 +143,11 @@ bool kvm_has_adjust_clock_stable(void) > >> >> return (ret == KVM_CLOCK_TSC_STABLE); > >> >> } > >> >> > >> >> +bool kvm_has_adjust_clock(void) > >> >> +{ > >> >> + return kvm_check_extension(kvm_state, KVM_CAP_ADJUST_CLOCK); > >> >> +} > >> >> + > >> >> bool kvm_has_exception_payload(void) > >> >> { > >> >> return has_exception_payload; > >> >> diff --git a/target/i386/kvm_i386.h b/target/i386/kvm_i386.h > >> >> index 064b8798a26c..0fce4e51d2d6 100644 > >> >> --- a/target/i386/kvm_i386.h > >> >> +++ b/target/i386/kvm_i386.h > >> >> @@ -34,6 +34,7 @@ > >> >> > >> >> bool kvm_allows_irq0_override(void); > >> >> bool kvm_has_smm(void); > >> >> +bool kvm_has_adjust_clock(void); > >> >> bool kvm_has_adjust_clock_stable(void); > >> >> bool kvm_has_exception_payload(void); > >> >> void kvm_synchronize_all_tsc(void); > >> >> -- > >> >> 2.25.4 > >> >> > >> >> > >> > >> -- > >> Vitaly > >> > > -- > Vitaly > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK