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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 D068FC433B4 for ; Thu, 6 May 2021 22:19:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A3E70613B5 for ; Thu, 6 May 2021 22:19:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230386AbhEFWUJ (ORCPT ); Thu, 6 May 2021 18:20:09 -0400 Received: from mga18.intel.com ([134.134.136.126]:57804 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230149AbhEFWUI (ORCPT ); Thu, 6 May 2021 18:20:08 -0400 IronPort-SDR: +Q+0ngws0Ovd65ndihcWDvzvcMwhoAngZF7yOigTzV4bu1hLsPPbkdDdnX8udE+0Ck7GXeS893 QmnlVJ46TqBA== X-IronPort-AV: E=McAfee;i="6200,9189,9976"; a="186055228" X-IronPort-AV: E=Sophos;i="5.82,279,1613462400"; d="scan'208";a="186055228" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 May 2021 15:19:09 -0700 IronPort-SDR: MjuSReAT0zksu9TbRtLbo+riDqZMvs+77DlWSL8zI6fHrRBOiU1Ckfv/6VBxEcjSuSytCnBWq4 3RcgjKORtQMA== X-IronPort-AV: E=Sophos;i="5.82,279,1613462400"; d="scan'208";a="465083907" Received: from sangbara-mobl.amr.corp.intel.com (HELO khuang2-desk.gar.corp.intel.com) ([10.209.86.237]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 May 2021 15:19:07 -0700 Message-ID: <613f09f72dc6f941771217eeb25f0193e021aebe.camel@intel.com> Subject: Re: [PATCH 3/3] KVM: x86/mmu: Fix TDP MMU page table level From: Kai Huang To: Ben Gardon Cc: kvm , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Date: Fri, 07 May 2021 10:19:04 +1200 In-Reply-To: References: <817eae486273adad0a622671f628c5a99b72a375.1620200410.git.kai.huang@intel.com> <51f7d6bbe52ad0c42d3c09fffd340fe7d2c0e113.camel@intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.0 (3.40.0-1.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 2021-05-06 at 09:23 -0700, Ben Gardon wrote: > On Thu, May 6, 2021 at 9:22 AM Ben Gardon wrote: > > > > On Thu, May 6, 2021 at 1:00 AM Kai Huang wrote: > > > > > > On Wed, 2021-05-05 at 09:28 -0700, Ben Gardon wrote: > > > > On Wed, May 5, 2021 at 2:38 AM Kai Huang wrote: > > > > > > > > > > TDP MMU iterator's level is identical to page table's actual level. For > > > > > instance, for the last level page table (whose entry points to one 4K > > > > > page), iter->level is 1 (PG_LEVEL_4K), and in case of 5 level paging, > > > > > the iter->level is mmu->shadow_root_level, which is 5. However, struct > > > > > kvm_mmu_page's level currently is not set correctly when it is allocated > > > > > in kvm_tdp_mmu_map(). When iterator hits non-present SPTE and needs to > > > > > allocate a new child page table, currently iter->level, which is the > > > > > level of the page table where the non-present SPTE belongs to, is used. > > > > > This results in struct kvm_mmu_page's level always having its parent's > > > > > level (excpet root table's level, which is initialized explicitly using > > > > > mmu->shadow_root_level). This is kinda wrong, and not consistent with > > > > > existing non TDP MMU code. Fortuantely the sp->role.level is only used > > > > > in handle_removed_tdp_mmu_page(), which apparently is already aware of > > > > > this, and handles correctly. However to make it consistent with non TDP > > > > > MMU code (and fix the issue that both root page table and any child of > > > > > it having shadow_root_level), fix this by using iter->level - 1 in > > > > > kvm_tdp_mmu_map(). Also modify handle_removed_tdp_mmu_page() to handle > > > > > such change. > > > > > > > > Ugh. Thank you for catching this. This is going to take me a bit to > > > > review as I should audit the code more broadly for this problem in the > > > > TDP MMU. > > > > It would probably also be a good idea to add a comment on the level > > > > field to say that it represents the level of the SPTEs in the > > > > associated page, not the level of the SPTE that links to the > > > > associated page. > > > > Hopefully that will prevent similar future misunderstandings. > > > > > > Regarding to adding a comment, sorry I had a hard time to figure out where to add. Did > > > you mean level field of 'struct kvm_mmu_page_role', or 'struct tdp_iter'? If it is the > > > former, to me not quite useful. > > > > I meant the level field of 'struct kvm_mmu_page_role', but if you > > don't think it makes sense to add one there, I don't feel strongly > > either way. > > > > > > > > I ended up with below. Is it OK to you? > > > > Yeah, it looks good to me. > > > > > > > > If you still think a comment of level should be added, would you be more specific so that > > > I can add it? > > > > struct { > > + /* > > + * The level of the SPT tracked by this SP, as opposed to the > > level of the > > + * parent SPTE linking this SPT. > > + */ > >         unsigned level:4; > > > > ... I guess that does sound kind of unnecessary. Thanks for explanation. It looks a little bit unnecessary for me. And if necessary, perhaps a separate patch :) > > > > > > > > ------------------------------------------------------------------------ > > > > > > TDP MMU iterator's level is identical to page table's actual level. For > > > instance, for the last level page table (whose entry points to one 4K > > > page), iter->level is 1 (PG_LEVEL_4K), and in case of 5 level paging, > > > the iter->level is mmu->shadow_root_level, which is 5. However, struct > > > kvm_mmu_page's level currently is not set correctly when it is allocated > > > in kvm_tdp_mmu_map(). When iterator hits non-present SPTE and needs to > > > allocate a new child page table, currently iter->level, which is the > > > level of the page table where the non-present SPTE belongs to, is used. > > > This results in struct kvm_mmu_page's level always having its parent's > > > level (excpet root table's level, which is initialized explicitly using > > > mmu->shadow_root_level). > > > > > > This is kinda wrong, and not consistent with existing non TDP MMU code. > > > Fortuantely sp->role.level is only used in handle_removed_tdp_mmu_page() > > > and kvm_tdp_mmu_zap_sp(), and they are already aware of this and behave > > > correctly. However to make it consistent with legacy MMU code (and fix > > > the issue that both root page table and its child page table have > > > shadow_root_level), use iter->level - 1 in kvm_tdp_mmu_map(), and change > > > handle_removed_tdp_mmu_page() and kvm_tdp_mmu_zap_sp() accordingly. > > > > > > Signed-off-by: Kai Huang > > Ooops, I meant to add: > > Reviewed-by: Ben Gardon Thank you! > > > > --- > > >  arch/x86/kvm/mmu/tdp_mmu.c | 8 ++++---- > > >  arch/x86/kvm/mmu/tdp_mmu.h | 2 +- > > >  2 files changed, 5 insertions(+), 5 deletions(-) > > > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > > index 5e28fbabcd35..45fb889f6a94 100644 > > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > > @@ -335,7 +335,7 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t > > > pt, > > > > > >         for (i = 0; i < PT64_ENT_PER_PAGE; i++) { > > >                 sptep = rcu_dereference(pt) + i; > > > - gfn = base_gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)); > > > + gfn = base_gfn + i * KVM_PAGES_PER_HPAGE(level); > > > > > >                 if (shared) { > > >                         /* > > > @@ -377,12 +377,12 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t > > > pt, > > >                         WRITE_ONCE(*sptep, REMOVED_SPTE); > > >                 } > > >                 handle_changed_spte(kvm, kvm_mmu_page_as_id(sp), gfn, > > > - old_child_spte, REMOVED_SPTE, level - 1, > > > + old_child_spte, REMOVED_SPTE, level, > > >                                     shared); > > >         } > > > > > >         kvm_flush_remote_tlbs_with_address(kvm, gfn, > > > - KVM_PAGES_PER_HPAGE(level)); > > > + KVM_PAGES_PER_HPAGE(level + 1)); > > > > > >         call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback); > > >  } > > > @@ -1013,7 +1013,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 > > > error_code, > > >                 } > > > > > >                 if (!is_shadow_present_pte(iter.old_spte)) { > > > - sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level); > > > + sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level - 1); > > >                         child_pt = sp->spt; > > > > > >                         new_spte = make_nonleaf_spte(child_pt, > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h > > > index 5fdf63090451..7f9974c5d0b4 100644 > > > --- a/arch/x86/kvm/mmu/tdp_mmu.h > > > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > > > @@ -31,7 +31,7 @@ static inline bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, > > >  } > > >  static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp) > > >  { > > > - gfn_t end = sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level); > > > + gfn_t end = sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level + 1); > > > > > >         /* > > >          * Don't allow yielding, as the caller may have a flush pending. Note, > > > -- > > > 2.31.1 > > > > > > > > > > > > > > > > > > > > Signed-off-by: Kai Huang > > > > > --- > > > > >  arch/x86/kvm/mmu/tdp_mmu.c | 8 ++++---- > > > > >  1 file changed, 4 insertions(+), 4 deletions(-) > > > > > > > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > > > > index debe8c3ec844..bcfb87e1c06e 100644 > > > > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > > > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > > > > @@ -335,7 +335,7 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t pt, > > > > > > > > > >         for (i = 0; i < PT64_ENT_PER_PAGE; i++) { > > > > >                 sptep = rcu_dereference(pt) + i; > > > > > - gfn = base_gfn + (i * KVM_PAGES_PER_HPAGE(level - 1)); > > > > > + gfn = base_gfn + i * KVM_PAGES_PER_HPAGE(level); > > > > > > > > > >                 if (shared) { > > > > >                         /* > > > > > @@ -377,12 +377,12 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t pt, > > > > >                         WRITE_ONCE(*sptep, REMOVED_SPTE); > > > > >                 } > > > > >                 handle_changed_spte(kvm, kvm_mmu_page_as_id(sp), gfn, > > > > > - old_child_spte, REMOVED_SPTE, level - 1, > > > > > + old_child_spte, REMOVED_SPTE, level, > > > > >                                     shared); > > > > >         } > > > > > > > > > >         kvm_flush_remote_tlbs_with_address(kvm, gfn, > > > > > - KVM_PAGES_PER_HPAGE(level)); > > > > > + KVM_PAGES_PER_HPAGE(level + 1)); > > > > > > > > > >         call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback); > > > > >  } > > > > > @@ -1009,7 +1009,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, > > > > >                 } > > > > > > > > > >                 if (!is_shadow_present_pte(iter.old_spte)) { > > > > > - sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level); > > > > > + sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level - 1); > > > > >                         child_pt = sp->spt; > > > > > > > > > >                         new_spte = make_nonleaf_spte(child_pt, > > > > > -- > > > > > 2.31.1 > > > > > > > > > > >