From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: KVM: VMX: fix incorrect cached cpl value with real/v8086 modes Date: Wed, 26 Dec 2012 15:33:16 +0200 Message-ID: <20121226133316.GI17584@redhat.com> References: <20121219132926.GA3551@amt.cnet> <20121225124808.GG17584@redhat.com> <20121225213710.GA5524@amt.cnet> <20121226052549.GA5149@redhat.com> <20121226132524.GA12758@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , kvm To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:13920 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753135Ab2LZNdS (ORCPT ); Wed, 26 Dec 2012 08:33:18 -0500 Content-Disposition: inline In-Reply-To: <20121226132524.GA12758@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Dec 26, 2012 at 11:25:24AM -0200, Marcelo Tosatti wrote: > On Wed, Dec 26, 2012 at 07:25:49AM +0200, Gleb Natapov wrote: > > On Tue, Dec 25, 2012 at 07:37:10PM -0200, Marcelo Tosatti wrote: > > > On Tue, Dec 25, 2012 at 02:48:08PM +0200, Gleb Natapov wrote: > > > > On Sat, Dec 22, 2012 at 02:31:10PM +0200, Avi Kivity wrote: > > > > > On Wed, Dec 19, 2012 at 3:29 PM, Marcelo Tosatti wrote: > > > > > > > > > > > > > > > > > > > > > > > CPL is always 0 when in real mode, and always 3 when virtual 8086 mode. > > > > > > > > > > > > Using values other than those can cause failures on operations that check > > > > > > CPL. > > > > > > > > > > > > Signed-off-by: Marcelo Tosatti > > > > > > > > > > > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > > > > > > index a4ecf7c..3abe433 100644 > > > > > > --- a/arch/x86/kvm/vmx.c > > > > > > +++ b/arch/x86/kvm/vmx.c > > > > > > @@ -3215,13 +3215,6 @@ static u64 vmx_get_segment_base(struct kvm_vcpu > > > > > > *vcpu, int seg) > > > > > > > > > > > > static int __vmx_get_cpl(struct kvm_vcpu *vcpu) > > > > > > { > > > > > > - if (!is_protmode(vcpu)) > > > > > > - return 0; > > > > > > - > > > > > > - if (!is_long_mode(vcpu) > > > > > > - && (kvm_get_rflags(vcpu) & X86_EFLAGS_VM)) /* if virtual 8086 > > > > > > */ > > > > > > - return 3; > > > > > > - > > > > > > return vmx_read_guest_seg_selector(to_vmx(vcpu), VCPU_SREG_CS) & 3; > > > > > > } > > > > > > > > > > > > @@ -3229,6 +3222,13 @@ static int vmx_get_cpl(struct kvm_vcpu *vcpu) > > > > > > { > > > > > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > > > > > > > > > > > + if (!is_protmode(vcpu)) > > > > > > + return 0; > > > > > > + > > > > > > + if (!is_long_mode(vcpu) > > > > > > + && (kvm_get_rflags(vcpu) & X86_EFLAGS_VM)) /* if virtual 8086 > > > > > > */ > > > > > > + return 3; > > > > > > + > > > > > > /* > > > > > > * If we enter real mode with cs.sel & 3 != 0, the normal CPL > > > > > > calculations > > > > > > * fail; use the cache instead. > > > > > > > > > > > > > > > > > > > > > This undoes the cache, now every vmx_get_cpl() in protected mode has to > > > > > VMREAD(GUEST_RFLAGS). > > > > True. Marcelo what failure do you see without the patch? > > > > > > > > -- > > > > Gleb. > > > > > > On transition _to_ real mode, linearize fails due to CPL checks > > > (FreeBSD). I'll resend the patch with use of cache for > > > VMREAD(GUEST_RFLAGS), which is already implemented. > > I am curious does it still fails with all my vmx patches applied too? > > Yes. > Which FreeBSD exactly? Cannot reproduce with FreeBSD 9 64 bits here. > > The question is how does it happen that we enter real mode while cache > > is set to 3. It should never be 3 during boot since boot process never > > enters the userspace. > > Its transition _to_ real mode (from protected). But in protected mode CPL should be 0 during boot. -- Gleb.