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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 8/6/25 21:18, Daniel P. Berrangé wrote: > 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. We can revert the commit. I'll send the revert to Stefan and let him decide whether to include it in 10.1-rc4 or delay to 10.2 and 10.1.1. Sorry for the delay in answering (and thanks Daniel for bringing this to my attention). Thanks, Paolo