From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422829AbbISRuE (ORCPT ); Sat, 19 Sep 2015 13:50:04 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:33320 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422820AbbISRtq (ORCPT ); Sat, 19 Sep 2015 13:49:46 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Paul Mackerras , Alexander Graf Subject: [PATCH 4.2 093/120] KVM: PPC: Book3S HV: Fix race in reading change bit when removing HPTE Date: Sat, 19 Sep 2015 10:28:53 -0700 Message-Id: <20150919171726.018270418@linuxfoundation.org> X-Mailer: git-send-email 2.5.3 In-Reply-To: <20150919171712.735441938@linuxfoundation.org> References: <20150919171712.735441938@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Mackerras commit 1e5bf454f58731e360e504253e85bae7aaa2d298 upstream. The reference (R) and change (C) bits in a HPT entry can be set by hardware at any time up until the HPTE is invalidated and the TLB invalidation sequence has completed. This means that when removing a HPTE, we need to read the HPTE after the invalidation sequence has completed in order to obtain reliable values of R and C. The code in kvmppc_do_h_remove() used to do this. However, commit 6f22bd3265fb ("KVM: PPC: Book3S HV: Make HTAB code LE host aware") removed the read after invalidation as a side effect of other changes. This restores the read of the HPTE after invalidation. The user-visible effect of this bug would be that when migrating a guest, there is a small probability that a page modified by the guest and then unmapped by the guest might not get re-transmitted and thus the destination might end up with a stale copy of the page. Fixes: 6f22bd3265fb Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -421,14 +421,20 @@ long kvmppc_do_h_remove(struct kvm *kvm, rev = real_vmalloc_addr(&kvm->arch.revmap[pte_index]); v = pte & ~HPTE_V_HVLOCK; if (v & HPTE_V_VALID) { - u64 pte1; - - pte1 = be64_to_cpu(hpte[1]); hpte[0] &= ~cpu_to_be64(HPTE_V_VALID); - rb = compute_tlbie_rb(v, pte1, pte_index); + rb = compute_tlbie_rb(v, be64_to_cpu(hpte[1]), pte_index); do_tlbies(kvm, &rb, 1, global_invalidates(kvm, flags), true); - /* Read PTE low word after tlbie to get final R/C values */ - remove_revmap_chain(kvm, pte_index, rev, v, pte1); + /* + * The reference (R) and change (C) bits in a HPT + * entry can be set by hardware at any time up until + * the HPTE is invalidated and the TLB invalidation + * sequence has completed. This means that when + * removing a HPTE, we need to re-read the HPTE after + * the invalidation sequence has completed in order to + * obtain reliable values of R and C. + */ + remove_revmap_chain(kvm, pte_index, rev, v, + be64_to_cpu(hpte[1])); } r = rev->guest_rpte & ~HPTE_GR_RESERVED; note_hpte_modification(kvm, rev);