From patchwork Sat Aug 22 09:21:30 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Graf X-Patchwork-Id: 7055381 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 1CD3A9F373 for ; Sat, 22 Aug 2015 09:22:33 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 43E28206A2 for ; Sat, 22 Aug 2015 09:22:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 530AB206A1 for ; Sat, 22 Aug 2015 09:22:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753402AbbHVJVi (ORCPT ); Sat, 22 Aug 2015 05:21:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:40500 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753311AbbHVJVh (ORCPT ); Sat, 22 Aug 2015 05:21:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9A1E5AD93; Sat, 22 Aug 2015 09:21:35 +0000 (UTC) From: Alexander Graf To: kvm-ppc Cc: KVM , Paolo Bonzini , Paul Mackerras Subject: [PULL 07/12] KVM: PPC: Book3S HV: Fix race in reading change bit when removing HPTE Date: Sat, 22 Aug 2015 11:21:30 +0200 Message-Id: <1440235295-244203-8-git-send-email-agraf@suse.de> X-Mailer: git-send-email 1.7.12.4 In-Reply-To: <1440235295-244203-1-git-send-email-agraf@suse.de> References: <1440235295-244203-1-git-send-email-agraf@suse.de> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-7.8 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Paul Mackerras 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 --- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index b027a89..c6d601c 100644 --- 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, unsigned long flags, 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);