From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753435AbbKIKOv (ORCPT ); Mon, 9 Nov 2015 05:14:51 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55779 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753410AbbKIKOp (ORCPT ); Mon, 9 Nov 2015 05:14:45 -0500 Subject: Re: [PATCH 5/5] KVM: x86: MMU: Consolidate WARN_ON/BUG_ON checks for reverse-mapped sptes To: Takuya Yoshikawa References: <20151106162016.6924957f7e227e52a345b061@lab.ntt.co.jp> <20151106162501.e97c5a05063625ed1a266553@lab.ntt.co.jp> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org From: Paolo Bonzini Message-ID: <5640720F.3080904@redhat.com> Date: Mon, 9 Nov 2015 11:14:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151106162501.e97c5a05063625ed1a266553@lab.ntt.co.jp> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/11/2015 08:25, Takuya Yoshikawa wrote: > At some call sites of rmap_get_first() and rmap_get_next(), BUG_ON is > placed right after the call to detect unrelated sptes which should not > be found in the reverse-mapping list. > > Move this check in rmap_get_first/next() so that all call sites, not > just the users of the for_each_rmap_spte() macro, will be checked the > same way. In addition, change the BUG_ON to WARN_ON since killing the > whole host is the last thing that KVM should try. > > One thing to keep in mind is that kvm_mmu_unlink_parents() also uses > rmap_get_first() to handle parent sptes. The change will not break it > because parent sptes are present, at least until drop_parent_pte() > actually unlinks them, and not mmio-sptes. Can you also change kvm_mmu_mark_parents_unsync to use for_each_rmap_spte instead of pte_list_walk? It is the last use of pte_list_walk, and it's nice if we have two uses of for_each_rmap_spte with parent_ptes as the argument. BTW, on my todo list is to change the rmap items to a struct (with a single u64 inside) for type safety. Since you are touching this code, perhaps you can give it a shot? Paolo > Signed-off-by: Takuya Yoshikawa > --- > Documentation/virtual/kvm/mmu.txt | 4 ++-- > arch/x86/kvm/mmu.c | 31 ++++++++++++++++++++++--------- > 2 files changed, 24 insertions(+), 11 deletions(-) > > diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt > index 3a4d681..daf9c0f 100644 > --- a/Documentation/virtual/kvm/mmu.txt > +++ b/Documentation/virtual/kvm/mmu.txt > @@ -203,10 +203,10 @@ Shadow pages contain the following information: > page cannot be destroyed. See role.invalid. > parent_ptes: > The reverse mapping for the pte/ptes pointing at this page's spt. If > - parent_ptes bit 0 is zero, only one spte points at this pages and > + parent_ptes bit 0 is zero, only one spte points at this page and > parent_ptes points at this single spte, otherwise, there exists multiple > sptes pointing at this page and (parent_ptes & ~0x1) points at a data > - structure with a list of parent_ptes. > + structure with a list of parent sptes. > unsync: > If true, then the translations in this page may not match the guest's > translation. This is equivalent to the state of the tlb when a pte is > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index c5e2363..353d752 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -1099,17 +1099,28 @@ struct rmap_iterator { > */ > static u64 *rmap_get_first(unsigned long rmap, struct rmap_iterator *iter) > { > + u64 *sptep; > + > if (!rmap) > return NULL; > > if (!(rmap & 1)) { > iter->desc = NULL; > - return (u64 *)rmap; > + sptep = (u64 *)rmap; > + goto out; > } > > iter->desc = (struct pte_list_desc *)(rmap & ~1ul); > iter->pos = 0; > - return iter->desc->sptes[iter->pos]; > + sptep = iter->desc->sptes[iter->pos]; > +out: > + /* > + * Parent sptes found in sp->parent_ptes lists are also checked here > + * since kvm_mmu_unlink_parents() uses this function. If the condition > + * needs to be changed for them, make another wrapper function. > + */ > + WARN_ON(!is_shadow_present_pte(*sptep)); > + return sptep; > } > > /* > @@ -1119,14 +1130,14 @@ static u64 *rmap_get_first(unsigned long rmap, struct rmap_iterator *iter) > */ > static u64 *rmap_get_next(struct rmap_iterator *iter) > { > + u64 *sptep; > + > if (iter->desc) { > if (iter->pos < PTE_LIST_EXT - 1) { > - u64 *sptep; > - > ++iter->pos; > sptep = iter->desc->sptes[iter->pos]; > if (sptep) > - return sptep; > + goto out; > } > > iter->desc = iter->desc->more; > @@ -1134,17 +1145,20 @@ static u64 *rmap_get_next(struct rmap_iterator *iter) > if (iter->desc) { > iter->pos = 0; > /* desc->sptes[0] cannot be NULL */ > - return iter->desc->sptes[iter->pos]; > + sptep = iter->desc->sptes[iter->pos]; > + goto out; > } > } > > return NULL; > +out: > + WARN_ON(!is_shadow_present_pte(*sptep)); > + return sptep; > } > > #define for_each_rmap_spte(_rmap_, _iter_, _spte_) \ > for (_spte_ = rmap_get_first(*_rmap_, _iter_); \ > - _spte_ && ({BUG_ON(!is_shadow_present_pte(*_spte_)); 1;}); \ > - _spte_ = rmap_get_next(_iter_)) > + _spte_; _spte_ = rmap_get_next(_iter_)) > > static void drop_spte(struct kvm *kvm, u64 *sptep) > { > @@ -1358,7 +1372,6 @@ static bool kvm_zap_rmapp(struct kvm *kvm, unsigned long *rmapp) > bool flush = false; > > while ((sptep = rmap_get_first(*rmapp, &iter))) { > - BUG_ON(!(*sptep & PT_PRESENT_MASK)); > rmap_printk("%s: spte %p %llx.\n", __func__, sptep, *sptep); > > drop_spte(kvm, sptep); >