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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 74E3BCEDD94 for ; Wed, 9 Oct 2024 13:45:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1syWzc-0001sG-4P; Wed, 09 Oct 2024 09:44:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1syWzZ-0001ru-Pz for qemu-devel@nongnu.org; Wed, 09 Oct 2024 09:44:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1syWzX-0004nZ-Oz for qemu-devel@nongnu.org; Wed, 09 Oct 2024 09:44:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1728481478; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hxSlVfdwjfarqvBks71oG7plJRRcCJoM0nP4bjc59ks=; b=iyWhfvQ3mKe8ELi16ltgm5Hl78Xtbh5Eg/4lAXTe/+OV+GCvLmCcYb5tSy/eOUWLAe/s61 nvY0CcgkdPwO3wWOgvbvJQg9J7mj+Zn0PRL2H9PI7NTjHBDzktu+5gayLPM8OgNbzoERiG QjuabEebQnZIKJAcQOv72O6vyzxtJH4= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-37-AQHXMEqwOVKbmxEgdMUg9A-1; Wed, 09 Oct 2024 09:44:36 -0400 X-MC-Unique: AQHXMEqwOVKbmxEgdMUg9A-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D50681956080; Wed, 9 Oct 2024 13:44:35 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.47]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A061919560AE; Wed, 9 Oct 2024 13:44:29 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id D2E6221E6A28; Wed, 9 Oct 2024 15:44:25 +0200 (CEST) From: Markus Armbruster To: Paolo Bonzini Cc: qemu-devel@nongnu.org, Richard Henderson , Eduardo Habkost , Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: x86 CPU properties "family", "model", "stepping", "tsc-freq" In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Wed, 9 Oct 2024 12:35:26 +0100") References: <87wmihr14b.fsf@pond.sub.org> Date: Wed, 09 Oct 2024 15:44:25 +0200 Message-ID: <871q0ppf0m.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.151, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Wed, Oct 09, 2024 at 01:01:40PM +0200, Markus Armbruster wrote: >> QOM properties serve several purposes: initial configuration (external >> interface), run time control and monitoring (external interface), and >> internal purposes like versioning. Which purpose(s) a property serves >> is often unclear. [...] >> Property "tsc-freq" seems not to be used internally. I figure changing >> it at run time makes no sense. Looks like it is be meant to be set by >> the user: x86_cpu_parse_featurestr() seems to parse it from the argument >> of -cpu. Correct? Note that -cpu help doesn't mention it. > > "tsc-freq" is a back compat alias for 'tsc-frequency' AFAICT, and > we need the latter if you want to guarantee fixed TSC freq across > migration. eg commit 561dbb41b1d752098249128d8462aaadc56fd15d Looking more closely... "tsc-freq" wraps around "tsc-frequency" except the value is converted with qemu_strtosz_metric(). "tsc-frequency" accepts values between 0 and INT64_MAX. The unit is Hz. However, the frequency is internally stored in kHz, in CPUArchState member tsc_khz, and the conversion from the value "tsc-frequency" silently truncates. Ugh! See x86_cpuid_set_tsc_freq(). kvm_arch_set_tsc_khz() passes the kHz value to the kernel like this: kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) I believe the kernel code consuming the value is in arch/x86/kvm/x86.c's kvm_arch_vcpu_ioctl(). It appears to silently truncate the value to 32 bit unsigned: case KVM_SET_TSC_KHZ: { u32 user_tsc_khz; r =3D -EINVAL; ---> user_tsc_khz =3D (u32)arg; if (kvm_caps.has_tsc_control && user_tsc_khz >=3D kvm_caps.max_guest_tsc_khz) goto out; if (user_tsc_khz =3D=3D 0) user_tsc_khz =3D tsc_khz; if (!kvm_set_tsc_khz(vcpu, user_tsc_khz)) r =3D 0; goto out; } Ugh again! Should we reject values exceeding UINT32_MAX kHz in QEMU?