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 E623CC87FCB for ; Wed, 6 Aug 2025 19:19:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ujjfH-0003kH-1M; Wed, 06 Aug 2025 15:19:07 -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 1ujjfF-0003je-47 for qemu-devel@nongnu.org; Wed, 06 Aug 2025 15:19:05 -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 1ujjfC-0006n5-Cp for qemu-devel@nongnu.org; Wed, 06 Aug 2025 15:19:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1754507939; 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=y/I2aVo3uOqEwJVvWHWYAMLDxxe2QbpW2QSyKxRFbj0=; b=VDNoR4hAWjbUe85cyTBUViR03pGk/u6bn7XwgVUA6ucfkagCA6DFPRUQQ3RGTtNIULoUDp mMzkJc4EXrVzvJenh9YMfUyWelaGUWSB7UCEEJV+3io+U/M5XLS7D+EKBb6i15B1x5rnji BStVlKYusqMg7i2kWg7oXhk2kuU1FDA= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-605--7PqZUnTPSS7fUL9OEAjJg-1; Wed, 06 Aug 2025 15:18:58 -0400 X-MC-Unique: -7PqZUnTPSS7fUL9OEAjJg-1 X-Mimecast-MFC-AGG-ID: -7PqZUnTPSS7fUL9OEAjJg_1754507937 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2DC1B1800359; Wed, 6 Aug 2025 19:18:57 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.15]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 60C101956086; Wed, 6 Aug 2025 19:18:55 +0000 (UTC) Date: Wed, 6 Aug 2025 20:18:51 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Christian Ehrhardt , Xiaoyao Li , Zhao Liu , Paolo Bonzini Cc: qemu-devel Subject: Re: Issues with pdcm in qemu 10.1-rc on migration and save/restore Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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, Aug 06, 2025 at 07:57:34PM +0200, Christian Ehrhardt wrote: > On Wed, Aug 6, 2025 at 2:00 PM Daniel P. Berrangé wrote: > > > > On Wed, Aug 06, 2025 at 01:52:17PM +0200, Christian Ehrhardt wrote: > > > Hi, > > > I was unsure if this would be better sent to libvirt or qemu - the > > > issue is somewhere between libvirt modelling CPUs and qemu 10.1 > > > behaving differently. I did not want to double post and gladly most of > > > the people are on both lists - since the switch in/out of the problem > > > is qemu 10.0 <-> 10.1 let me start here. I beg your pardon for not yet > > > having all the answers, I'm sure I could find more with debugging, but > > > I also wanted to report early for your awareness while we are still in > > > the RC phase. > > > > > > > > > # Problem > > > > > > What I found when testing migrations in Ubuntu with qemu 10.1-rc1 was: > > > error: operation failed: guest CPU doesn't match specification: > > > missing features: pdcm > > > > > > This is behaving the same with libvirt 11.4 or the more recent 11.6. > > > But switching back to qemu 10.0 confirmed that this behavior is new > > > with qemu 10.1-rc. > > > > > > > Without yet having any hard evidence against them I found a few pdcm > > > related commits between 10.0 and 10.1-rc1: > > > 7ff24fb65 i386/tdx: Don't mask off CPUID_EXT_PDCM > > > 00268e000 i386/cpu: Warn about why CPUID_EXT_PDCM is not available > > > e68ec2980 i386/cpu: Move adjustment of CPUID_EXT_PDCM before > > > feature_dependencies[] check > > > 0ba06e46d i386/tdx: Add TDX fixed1 bits to supported CPUIDs > > > > > > > > > # Caveat > > > > > > My test environment is in LXD system containers, that gives me issues > > > in the power management detection > > > libvirtd[406]: error from service: GDBus.Error:System.Error.EROFS: > > > Read-only file system > > > libvirtd[406]: Failed to get host power management capabilities > > > > That's harmless. > > Yeah, it always was for me - thanks for confirming. > > > > And the resulting host-model on a rather old test server will therefore have: > > > > > > Haswell-noTSX-IBRS > > > Intel > > > > > > > > > ... > > > > > > But that was fine in the past, and the behavior started to break > > > save/restore or migrations just now with the new qemu 10.1-rc. > > > > > > # Next steps > > > > > > I'm soon overwhelmed by meetings for the rest of the day, but would be > > > curious if one has a suggestion about what to look at next for > > > debugging or a theory about what might go wrong. If nothing else comes > > > up I'll try to set up a bisect run tomorrow. > > > > Yeah, git bisect is what I'd start with. > > Bisect complete, identified this commit > > commit 00268e00027459abede448662f8794d78eb4b0a4 > Author: Xiaoyao Li > Date: Tue Mar 4 00:24:50 2025 -0500 > > i386/cpu: Warn about why CPUID_EXT_PDCM is not available > > When user requests PDCM explicitly via "+pdcm" without PMU enabled, emit > a warning to inform the user. > > Signed-off-by: Xiaoyao Li > Reviewed-by: Zhao Liu > Link: https://lore.kernel.org/r/20250304052450.465445-3-xiaoyao.li@intel.com > Signed-off-by: Paolo Bonzini > > target/i386/cpu.c | 3 +++ > 1 file changed, 3 insertions(+) > > > > Which is odd as it should only add a warning right? No, that commit message is misleading. IIUC mark_unavailable_features() actively blocks usage of the feature, so it is a functional change, not merely a emitting warning. It makes me wonder if that commit was actually intended to block the feature or not, vs merely warning ? CC'ing those involved in the commit. 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 :|