From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liran Alon Subject: Re: [PATCH] KVM: nVMX/nSVM: Don't intercept #UD when running L2 Date: Mon, 06 Nov 2017 13:02:05 +0200 Message-ID: <5A00412D.60604@ORACLE.COM> References: <1509898543-11835-1-git-send-email-liran.alon@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: jmattson@google.com, idan.brown@ORACLE.COM, Konrad Rzeszutek Wilk To: Paolo Bonzini , rkrcmar@redhat.com, kvm@vger.kernel.org Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:29114 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751457AbdKFLCV (ORCPT ); Mon, 6 Nov 2017 06:02:21 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 06/11/17 11:27, Paolo Bonzini wrote: > On 05/11/2017 17:15, Liran Alon wrote: >> When running L2, #UD should be intercepted by L1 or just forwarded >> directly to L2. It should not reach L0 x86 emulator. >> Therefore, set intercept for #UD only based on L1 exception-bitmap. >> >> Also add BUG_ON() on L0 #UD intercept handlers to make sure it is never >> reached while running L2. >> >> This improves commit ae1f57670703 ("KVM: nVMX: Do not emulate #UD while >> in guest mode") by removing an unnecessary exit from L2 to L0 on #UD >> when L1 doesn't intercept it. >> >> In addition, SVM L0 #UD intercept handler doesn't handle correctly the >> case it is raised from L2. In this case, it should forward the #UD to >> guest instead of x86 emulator. As done in VMX #UD intercept handler. >> This commit fixes this issue as-well. >> >> Signed-off-by: Liran Alon >> Reviewed-by: Nikita Leshenko >> Reviewed-by: Konrad Rzeszutek Wilk >> Signed-off-by: Konrad Rzeszutek Wilk >> --- >> arch/x86/kvm/svm.c | 4 +++- >> arch/x86/kvm/vmx.c | 9 ++++----- >> 2 files changed, 7 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c >> index 0e68f0b3cbf7..1c7f76a417e7 100644 >> --- a/arch/x86/kvm/svm.c >> +++ b/arch/x86/kvm/svm.c >> @@ -1221,7 +1221,8 @@ static void init_vmcb(struct vcpu_svm *svm) >> set_dr_intercepts(svm); >> >> set_exception_intercept(svm, PF_VECTOR); >> - set_exception_intercept(svm, UD_VECTOR); >> + if (!is_guest_mode(&svm->vcpu)) >> + set_exception_intercept(svm, UD_VECTOR); >> set_exception_intercept(svm, MC_VECTOR); >> set_exception_intercept(svm, AC_VECTOR); >> set_exception_intercept(svm, DB_VECTOR); > > This is not called on every vmexit. The right place to touch is > recalc_intercepts. Then on vmexit it will be automatically restored > when nested_svm_vmexit calls copy_vmcb_control_area. Agreed. My bad. Will fix in v2 of this commit. > >> @@ -2188,6 +2189,7 @@ static int ud_interception(struct vcpu_svm *svm) >> { >> int er; >> >> + BUG_ON(is_guest_mode(&svm->vcpu)); >> er = emulate_instruction(&svm->vcpu, EMULTYPE_TRAP_UD); >> if (er != EMULATE_DONE) >> kvm_queue_exception(&svm->vcpu, UD_VECTOR); >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 95a01609d7ee..5e2c47dd0c83 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -1878,7 +1878,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) >> { >> u32 eb; >> >> - eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) | >> + eb = (1u << PF_VECTOR) | (1u << MC_VECTOR) | >> (1u << DB_VECTOR) | (1u << AC_VECTOR); >> if ((vcpu->guest_debug & >> (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) == >> @@ -1896,6 +1896,8 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) >> */ >> if (is_guest_mode(vcpu)) >> eb |= get_vmcs12(vcpu)->exception_bitmap; >> + else >> + eb |= 1u << UD_VECTOR; > > It's a nit, but since you have to send a v2, I'd prefer to keep > UD_VECTOR above and clear it here. I think your suggestion could be problematic. In case (to_vmx(vcpu)->rmode.vm86_active == true) then we would like to intercept all exceptions and therefore not clear UD_VECTOR. This is why I preferred this approach. > > Thanks, > > Paolo > >> vmcs_write32(EXCEPTION_BITMAP, eb); >> } >> @@ -5881,10 +5883,7 @@ static int handle_exception(struct kvm_vcpu *vcpu) >> return 1; /* already handled by vmx_vcpu_run() */ >> >> if (is_invalid_opcode(intr_info)) { >> - if (is_guest_mode(vcpu)) { >> - kvm_queue_exception(vcpu, UD_VECTOR); >> - return 1; >> - } >> + BUG_ON(is_guest_mode(vcpu)); >> er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD); >> if (er != EMULATE_DONE) >> kvm_queue_exception(vcpu, UD_VECTOR); >> >