From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v2] kvm: x86: emulate monitor and mwait instructions as nop Date: Wed, 4 Jun 2014 22:08:12 +0300 Message-ID: <20140604190812.GG11756@redhat.com> References: <20140507205210.GA30030@ERROL.INI.CMU.EDU> <20140602192530.GC1653@ERROL.INI.CMU.EDU> <538D92BC.4060203@redhat.com> <20140604143941.GF1653@ERROL.INI.CMU.EDU> <538F30BD.5000501@suse.de> <538F4A7C.7070202@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alexander Graf , "Gabriel L. Somlo" , kvm@vger.kernel.org, Borislav Petkov To: Paolo Bonzini Return-path: Received: from mx1.redhat.com ([209.132.183.28]:7411 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750925AbaFDTIE (ORCPT ); Wed, 4 Jun 2014 15:08:04 -0400 Content-Disposition: inline In-Reply-To: <538F4A7C.7070202@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Jun 04, 2014 at 06:34:04PM +0200, Paolo Bonzini wrote: > Il 04/06/2014 16:44, Alexander Graf ha scritto: > > > > > >>Obviously, if you really like the current behavior better you can > >>always reject whatever patch I'll come up with, but I'd like to at > >>least try and see what it would look like :) > > > >I think it's perfectly fine to leave mwait always implemented as NOP - > >it's valid behavior. > > > >As for the CPUID exposure, that should be a pure QEMU thing. If > >overriding CPUID bits the kernel mask tells us doesn't work today, we > >should just make it possible :). > > That should be the purpose of KVM_GET_EMULATED_CPUID, so MWAIT could be > added in __do_cpuid_ent_emulated. However, the corresponding QEMU patches > were never included. Borislav, can you refresh them? > > Paolo I don't understand why would we want mwait bit set in CPUID. The only reason we want the nop is because of broken guests which don't check CPUID. -- MST