From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2 0/3] Fix task switches into/out of VM86 Date: Mon, 30 Jan 2012 13:59:34 +0200 Message-ID: <4F268626.5090209@redhat.com> References: <1327692216-20450-1-git-send-email-kwolf@redhat.com> <20120127195239.GB2938@redhat.com> <4F265961.3070501@redhat.com> <20120130085541.GI30469@redhat.com> <4F267254.7040900@redhat.com> <4F2674BB.2000608@redhat.com> <20120130105022.GC23536@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Kevin Wolf , kvm@vger.kernel.org, joerg.roedel@amd.com, yoshikawa.takuya@oss.ntt.co.jp, mtosatti@redhat.com To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49555 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752275Ab2A3L7k (ORCPT ); Mon, 30 Jan 2012 06:59:40 -0500 In-Reply-To: <20120130105022.GC23536@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/30/2012 12:50 PM, Gleb Natapov wrote: > On Mon, Jan 30, 2012 at 12:45:15PM +0200, Avi Kivity wrote: > > On 01/30/2012 12:35 PM, Kevin Wolf wrote: > > > Am 30.01.2012 09:55, schrieb Gleb Natapov: > > > > On Mon, Jan 30, 2012 at 09:48:33AM +0100, Kevin Wolf wrote: > > > >> Am 27.01.2012 20:52, schrieb Gleb Natapov: > > > >>> On Fri, Jan 27, 2012 at 08:23:33PM +0100, Kevin Wolf wrote: > > > >>>> I believe this should work with both VMX and SVM now. Gleb, = J=C3=B6rg, can one of > > > >>>> you test this with SVM? I did some testing on my buggy proce= ssor and it looks > > > >>>> as good as it gets, but it would be better if you could conf= irm. > > > >>>> > > > >>> You forgot to set cpl to 3 in vmcb in svm_set_rflags() when v= m86 is enabled, no? > > > >> > > > >> SVM updates the CPL when the segment selector for CS is loaded= =2E From a > > > >> svm.c POV, segment selectors are updated immediately after set= _rflags, > > > >> so it wouldn't really make a difference to do it twice. > > > >> > > > > It is too subtle to rely on that. The fact is that checking cpl= after > > > > set_rflags provides incorrect value. This better be fixed. > > > > > > Depends on what value you consider to be correct between reloadin= g > > > eflags and reloading cs. I think it's logical and more consistent= to say > > > that CPL only changes when cs is reloaded, but you could argue th= at it's > > > effective with the reload of rflags. It doesn't make a difference= to > > > guests, so we can decide to choose whatever we like. > >=20 > > It's best to make it independent (like svm, and force vmx to emulat= e > > this behaviour). Real mode forces cpl to 0, vm86 forces cpl to 3, > > protected mode (and I think long mode) uses cs.rpl. > This is what vmx does, not svm.=20 That's the architectural definition, except for mode switch sequences.=20 vmx implements it directly which means that mode switch sequences sometimes fail, either in guest software (setting cr0.pe while cs & 3 != =3D 0) or in "microcode" (emulate.c). > svm checks vmcb->cpl that can be > outdated during emulation. This decoupling is actually helpful, since you can defer the cpl change until the end of the switch, and avoid inconsistencies like those checked by cs_ss_rpl_check(). --=20 error compiling committee.c: too many arguments to function