From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mackerras Date: Fri, 24 Apr 2015 05:39:05 +0000 Subject: [PATCH 1/3] KVM: PPC: Book3S HV: Fix race in reading change bit when removing HPTE Message-Id: <1429853947-30681-2-git-send-email-paulus@samba.org> List-Id: References: <1429853947-30681-1-git-send-email-paulus@samba.org> In-Reply-To: <1429853947-30681-1-git-send-email-paulus@samba.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kvm-ppc@vger.kernel.org, kvm@vger.kernel.org Cc: Nathan Whitehorn 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 Cc: stable@vger.kernel.org # v3.17+ Signed-off-by: Paul Mackerras --- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index f6bf0b1..5c1737f 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -413,14 +413,12 @@ 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); + 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); -- 2.1.4