From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752657AbbKYPpl (ORCPT ); Wed, 25 Nov 2015 10:45:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48008 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751704AbbKYPpi (ORCPT ); Wed, 25 Nov 2015 10:45:38 -0500 From: Bandan Das To: Haozhong Zhang Cc: kvm@vger.kernel.org, Gleb Natapov , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: nVMX: remove incorrect vpid check in nested invvpid emulation References: <1448443299-9375-1-git-send-email-haozhong.zhang@intel.com> Date: Wed, 25 Nov 2015 10:45:36 -0500 In-Reply-To: <1448443299-9375-1-git-send-email-haozhong.zhang@intel.com> (Haozhong Zhang's message of "Wed, 25 Nov 2015 17:21:39 +0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Haozhong Zhang writes: > This patch removes the vpid check when emulating nested invvpid > instruction of type all-contexts invalidation. The existing code is > incorrect because: > (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate > Translations Based on VPID", invvpid instruction does not check > vpid in the invvpid descriptor when its type is all-contexts > invalidation. But iirc isn't vpid=0 reserved for root mode ? I think we don't want L1 hypervisor to be able do a invvpid(0). > (2) According to the same document, invvpid of type all-contexts > invalidation does not require there is an active VMCS, so/and > get_vmcs12() in the existing code may result in a NULL-pointer > dereference. In practice, it can crash both KVM itself and L1 > hypervisors that use invvpid (e.g. Xen). If that is the case, then just check if it's null and return without doing anything. > Signed-off-by: Haozhong Zhang > --- > arch/x86/kvm/vmx.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 87acc52..af823a3 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) > > switch (type) { > case VMX_VPID_EXTENT_ALL_CONTEXT: > - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { > - nested_vmx_failValid(vcpu, > - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); > - return 1; > - } > __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); > nested_vmx_succeed(vcpu); > break; I also noticed a BUG() here in the default. It might be a good idea to replace it with a WARN.