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 71323CEDD95 for ; Wed, 9 Oct 2024 13:48:48 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1syX2s-0002zG-Ou; Wed, 09 Oct 2024 09:48:07 -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 1syX2o-0002yi-SM for qemu-devel@nongnu.org; Wed, 09 Oct 2024 09:48:02 -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 1syX2n-00059u-6k for qemu-devel@nongnu.org; Wed, 09 Oct 2024 09:48:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1728481678; h=from:from:reply-to: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=kjH/P/g2QKpC8+ixdPp3xnRGLyP1oTyCqIlBOSjcPAQ=; b=YgUQm06ZRFgiRuBCjRDeUmPTntylshfGV/4VSFyakv2uTX4NwEDsSvPn04St+nD75R0Iwq 2YDyEx1xg/5hM5To6+2cOyb0Kpx04R+7AjxIORv0IRpUyXkQ3kl8RB15tBotYoHR0pd3sj oz+Tetdq6a/HaskdjNWY841pyuJpOIo= Received: from mx-prod-mc-01.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-179-I4T5K-KuPdmMtE2eIcmDmw-1; Wed, 09 Oct 2024 09:47:57 -0400 X-MC-Unique: I4T5K-KuPdmMtE2eIcmDmw-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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DCC671956077; Wed, 9 Oct 2024 13:47:55 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.112]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1C08619560AA; Wed, 9 Oct 2024 13:47:52 +0000 (UTC) Date: Wed, 9 Oct 2024 14:47:49 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: Paolo Bonzini , qemu-devel@nongnu.org, Richard Henderson , Eduardo Habkost Subject: Re: x86 CPU properties "family", "model", "stepping", "tsc-freq" Message-ID: References: <87wmihr14b.fsf@pond.sub.org> <871q0ppf0m.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <871q0ppf0m.fsf@pond.sub.org> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Oct 09, 2024 at 03:44:25PM +0200, Markus Armbruster wrote: > Daniel P. Berrangé 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 = -EINVAL; > ---> user_tsc_khz = (u32)arg; > > if (kvm_caps.has_tsc_control && > user_tsc_khz >= kvm_caps.max_guest_tsc_khz) > goto out; > > if (user_tsc_khz == 0) > user_tsc_khz = tsc_khz; > > if (!kvm_set_tsc_khz(vcpu, user_tsc_khz)) > r = 0; > > goto out; > } > > Ugh again! > > Should we reject values exceeding UINT32_MAX kHz in QEMU? Sounds like a reasonable idea to me, as I don't think it is very likely that someone is passing a number greater than UINT32_MAX and relying on truncation. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|