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 287DCC54FCF for ; Mon, 23 Mar 2020 16:50:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 043742072D for ; Mon, 23 Mar 2020 16:50:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727641AbgCWQuD (ORCPT ); Mon, 23 Mar 2020 12:50:03 -0400 Received: from mga02.intel.com ([134.134.136.20]:36306 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727067AbgCWQuD (ORCPT ); Mon, 23 Mar 2020 12:50:03 -0400 IronPort-SDR: AuCpJwR6e+ND5waOSVyALQJStdbEozrPuOUoz/2Mxvlrcu1zQ1eQBxNe6dslk0xrCuFupYLwkT TTZ8E36hxLXg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2020 09:50:02 -0700 IronPort-SDR: YOjnM1lhGB6aAHFakbm39vv7nwcKvrPIL1qKbD+3OLR+h+dn9jhdjj/+lZlvnev8270tbaFZmK d5gqoSd7NAcQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,297,1580803200"; d="scan'208";a="447452716" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga006.fm.intel.com with ESMTP; 23 Mar 2020 09:50:01 -0700 Date: Mon, 23 Mar 2020 09:50:01 -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 04/37] KVM: nVMX: Invalidate all roots when emulating INVVPID without EPT Message-ID: <20200323165001.GR28711@linux.intel.com> References: <20200320212833.3507-1-sean.j.christopherson@intel.com> <20200320212833.3507-5-sean.j.christopherson@intel.com> <87v9mv84qu.fsf@vitty.brq.redhat.com> <20200323160432.GJ28711@linux.intel.com> <87lfnr820r.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87lfnr820r.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 05:33:08PM +0100, Vitaly Kuznetsov wrote: > Sean Christopherson writes: > > > On Mon, Mar 23, 2020 at 04:34:17PM +0100, Vitaly Kuznetsov wrote: > >> Sean Christopherson writes: > >> > >> > From: Junaid Shahid > >> > > >> > Free all roots when emulating INVVPID for L1 and EPT is disabled, as > >> > outstanding changes to the page tables managed by L1 need to be > >> > recognized. Because L1 and L2 share an MMU when EPT is disabled, and > >> > because VPID is not tracked by the MMU role, all roots in the current > >> > MMU (root_mmu) need to be freed, otherwise a future nested VM-Enter or > >> > VM-Exit could do a fast CR3 switch (without a flush/sync) and consume > >> > stale SPTEs. > >> > > >> > Fixes: 5c614b3583e7b ("KVM: nVMX: nested VPID emulation") > >> > Signed-off-by: Junaid Shahid > >> > [sean: ported to upstream KVM, reworded the comment and changelog] > >> > Signed-off-by: Sean Christopherson > >> > --- > >> > arch/x86/kvm/vmx/nested.c | 14 ++++++++++++++ > >> > 1 file changed, 14 insertions(+) > >> > > >> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > >> > index 9624cea4ed9f..bc74fbbf33c6 100644 > >> > --- a/arch/x86/kvm/vmx/nested.c > >> > +++ b/arch/x86/kvm/vmx/nested.c > >> > @@ -5250,6 +5250,20 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) > >> > return kvm_skip_emulated_instruction(vcpu); > >> > } > >> > > >> > + /* > >> > + * Sync the shadow page tables if EPT is disabled, L1 is invalidating > >> > + * linear mappings for L2 (tagged with L2's VPID). Free all roots as > >> > + * VPIDs are not tracked in the MMU role. > >> > + * > >> > + * Note, this operates on root_mmu, not guest_mmu, as L1 and L2 share > >> > + * an MMU when EPT is disabled. > >> > + * > >> > + * TODO: sync only the affected SPTEs for INVDIVIDUAL_ADDR. > >> > + */ > >> > + if (!enable_ept) > >> > + kvm_mmu_free_roots(vcpu, &vcpu->arch.root_mmu, > >> > + KVM_MMU_ROOTS_ALL); > >> > + > >> > >> This is related to my remark on the previous patch; the comment above > >> makes me think I'm missing something obvious, enlighten me please) > >> > >> My understanding is that L1 and L2 will share arch.root_mmu not only > >> when EPT is globally disabled, we seem to switch between > >> root_mmu/guest_mmu only when nested_cpu_has_ept(vmcs12) but different L2 > >> guests may be different on this. Do we need to handle this somehow? > > > > guest_mmu is used iff nested EPT is enabled, which requires enable_ept=1. > > enable_ept is global and cannot be changed without reloading kvm_intel. > > > > This most definitely over-invalidates, e.g. it blasts away L1's page > > tables. But, fixing that requires tracking VPID in mmu_role and/or adding > > support for using guest_mmu when L1 isn't using TDP, i.e. nested EPT is > > disabled. Assuming the vast majority of nested deployments enable EPT in > > L0, the cost of both options likely outweighs the benefits. > > > > Yes but my question rather was: what if global 'enable_ept' is true but > nested EPT is not being used by L1, don't we still need to do > kvm_mmu_free_roots(&vcpu->arch.root_mmu) here? No, because L0 isn't shadowing the L1->L2 page tables, i.e. there can't be unsync'd SPTEs for L2. The vpid_sync_*() above flushes the TLB for L2's effective VPID, which is all that's required.