From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [BISECTED REGRESSION] v4.0+ KVM: x86: allow TSC deadline timer on all hosts Date: Wed, 8 Feb 2017 17:29:04 +0100 Message-ID: <6f8284c8-eb4b-3f90-6a34-4361b8194809@redhat.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , Radim Krcmar , kvm To: "Matwey V. Kornilov" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:44460 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752056AbdBHQjZ (ORCPT ); Wed, 8 Feb 2017 11:39:25 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 08/02/2017 17:26, Matwey V. Kornilov wrote: > 2017-02-08 11:50 GMT+03:00 Paolo Bonzini : >> On 07/02/2017 21:43, Matwey V. Kornilov wrote: >>> I am not sure that user-space behavior should change. Also I am not >>> sure that qemu should show unsupported CPU flags to guests. >> >> Userspace behavior changed only because you used "-cpu host". "-cpu >> host" tells QEMU to enable everything the kernel can enable, so it can >> break when you update the host kernel. >> >> Without "-cpu host" (e.g. "-cpu Nehalem"), either there would have been >> no change in behavior, or you'd have had a warning before >> >> warning: host doesn't support requested feature: >> CPUID.1H:ECX.tsc_deadline_timer [bit 24] > > -cpu host,-tsc-deadline also works. > >> and no warning afterwards. Is this with KVM nested under VMware, as in >> your launchpad bug report? > > Yes. It is nested under VMware. So the root cause here is that Linux doesn't like VMware's TSC. Paolo