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Wed, 06 Aug 2025 10:58:01 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHZxfw6Qa3Ye1UyJcqtskbVygx1yLoeOfp5rMp6pnD8G0oV3J788DropTF++k9kJ1K+kKhtR2d66UAWN1B4dXU= X-Received: by 2002:a05:6402:274c:b0:60e:23d:43b1 with SMTP id 4fb4d7f45d1cf-6179615a422mr3412842a12.16.1754503080596; Wed, 06 Aug 2025 10:58:00 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Christian Ehrhardt Date: Wed, 6 Aug 2025 19:57:34 +0200 X-Gm-Features: Ac12FXwzNQaPv4CP1-TlHtIttj99qJlIgo4YL8oWn0UtBTSlxNCefl3MyqD8zhc Message-ID: Subject: Re: Issues with pdcm in qemu 10.1-rc on migration and save/restore To: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: qemu-devel Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=185.125.188.123; envelope-from=christian.ehrhardt@canonical.com; helo=smtp-relay-internal-1.canonical.com X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 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_MED=-2.3, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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 On Wed, Aug 6, 2025 at 2:00=E2=80=AFPM Daniel P. Berrang=C3=A9 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 therefor= e 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, emi= t 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@inte= l.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? But I checked the logs - the build on "e68ec29809 i386/cpu: Move adjustment of CPUID_EXT_PDCM before feature_dependencies[] check" passed the same use case. I'll build both outside of the bisect run tomorrow to ensure this is reproducible when I watch it more closely (than submitting a bisect script). Maybe this already helps to put your eyes and thoughts in the right directi= on. > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| > |: https://libvirt.org -o- https://fstop138.berrange.c= om :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :| > --=20 Christian Ehrhardt Director of Engineering, Ubuntu Server Canonical Ltd