From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 536E2C54EEB for ; Mon, 23 Mar 2020 15:53:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 34B5620719 for ; Mon, 23 Mar 2020 15:53:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727443AbgCWPxI (ORCPT ); Mon, 23 Mar 2020 11:53:08 -0400 Received: from mga02.intel.com ([134.134.136.20]:31439 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbgCWPxI (ORCPT ); Mon, 23 Mar 2020 11:53:08 -0400 IronPort-SDR: ncCw1rb1HEuIF2ENAe6XXQnykfbc1Y80MZaoaU4K8/tHy2lybNsopecy3qxJeQmslQIkdgeXJh BfboVzPgbcgw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2020 08:53:07 -0700 IronPort-SDR: LIJXRONbRlBxcoQXcsZECJpyRHFeeku3lkFQLFDecL3Xga5yGR57rgWcvcL18VIT8QTcJfP+sk 06mjAFwHKiLg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,296,1580803200"; d="scan'208";a="445858372" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga005.fm.intel.com with ESMTP; 23 Mar 2020 08:53:05 -0700 Date: Mon, 23 Mar 2020 08:53:05 -0700 From: Sean Christopherson To: Vitaly Kuznetsov Cc: Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon , Junaid Shahid , Liran Alon , Boris Ostrovsky , John Haxby , Miaohe Lin , Tom Lendacky Subject: Re: [PATCH v3 03/37] KVM: nVMX: Invalidate all EPTP contexts when emulating INVEPT for L1 Message-ID: <20200323155305.GI28711@linux.intel.com> References: <20200320212833.3507-1-sean.j.christopherson@intel.com> <20200320212833.3507-4-sean.j.christopherson@intel.com> <87y2rr857u.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y2rr857u.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Mar 23, 2020 at 04:24:05PM +0100, Vitaly Kuznetsov wrote: > Sean Christopherson writes: > > > Free all L2 (guest_mmu) roots when emulating INVEPT for L1. Outstanding > > changes to the EPT tables managed by L1 need to be recognized, and > > relying on KVM to always flush L2's EPTP context on nested VM-Enter is > > dangerous. > > > > Similar to handle_invpcid(), rely on kvm_mmu_free_roots() to do a remote > > TLB flush if necessary, e.g. if L1 has never entered L2 then there is > > nothing to be done. > > > > Nuking all L2 roots is overkill for the single-context variant, but it's > > the safe and easy bet. A more precise zap mechanism will be added in > > the future. Add a TODO to call out that KVM only needs to invalidate > > affected contexts. > > > > Fixes: b119019847fbc ("kvm: nVMX: Remove unnecessary sync_roots from handle_invept") > > Reported-by: Jim Mattson > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/vmx/nested.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > > index f3774cef4fd4..9624cea4ed9f 100644 > > --- a/arch/x86/kvm/vmx/nested.c > > +++ b/arch/x86/kvm/vmx/nested.c > > @@ -5160,12 +5160,12 @@ static int handle_invept(struct kvm_vcpu *vcpu) > > if (!nested_vmx_check_eptp(vcpu, operand.eptp)) > > return nested_vmx_failValid(vcpu, > > VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); > > + > > + /* TODO: sync only the target EPTP context. */ > > fallthrough; > > case VMX_EPT_EXTENT_GLOBAL: > > - /* > > - * TODO: Sync the necessary shadow EPT roots here, rather than > > - * at the next emulated VM-entry. > > - */ > > + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, > > + KVM_MMU_ROOTS_ALL); > > break; > > An ignorant reader may wonder "and how do we know that L1 actaully uses > EPT" as he may find out that guest_mmu is not being used otherwise. The > answer to the question will likely be "if L1 doesn't use EPT for some of > its guests than there's nothing we should do here as we will be > resetting root_mmu when switching to/from them". Hope the ignorant > reviewer typing this is not very wrong :-) A different way to put it would be: KVM never uses root_mmu to hold nested EPT roots. Invalidating too much is functionally ok, though sub-optimal for performance. Invalidating too little is what we really care about. FWIW, VMX currently uses guest_mmu iff nested EPT is enabled. In theory, KVM could be enhanced to also used guest_mmu when nested-TDP is disabled, e.g. to enable VMX to preserve L1's root_mmu when emulating INVVPID. That would likely be a decent performance boost for nested VMX+VPID without nested EPT, but I'm guessing that the cross-section of users that care about nested performance and don't use nested EPT is quite small. > > default: > > BUG_ON(1); > > Reviewed-by: Vitaly Kuznetsov > > -- > Vitaly >