From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41bgz10Q4VzDqnG for ; Thu, 26 Jul 2018 15:44:45 +1000 (AEST) Date: Thu, 26 Jul 2018 15:44:34 +1000 From: Paul Mackerras To: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: Sam Bobroff , David Gibson Subject: [PATCH 2/2] KVM: PPC: Book3S HV: Read kvm->arch.emul_smt_mode under kvm->lock Message-ID: <20180726054434.GC1672@fergus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Commit 1e175d2 ("KVM: PPC: Book3S HV: Pack VCORE IDs to access full VCPU ID space", 2018-07-25) added code that uses kvm->arch.emul_smt_mode before any VCPUs are created. However, userspace can change kvm->arch.emul_smt_mode at any time up until the first VCPU is created. Hence it is (theoretically) possible for the check in kvmppc_core_vcpu_create_hv() to race with another userspace thread changing kvm->arch.emul_smt_mode. This fixes it by moving the test that uses kvm->arch.emul_smt_mode into the block where kvm->lock is held. Signed-off-by: Paul Mackerras --- arch/powerpc/kvm/book3s_hv.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 785245e..113f815 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -1989,16 +1989,10 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm, unsigned int id) { struct kvm_vcpu *vcpu; - int err = -EINVAL; + int err; int core; struct kvmppc_vcore *vcore; - if (id >= (KVM_MAX_VCPUS * kvm->arch.emul_smt_mode) && - cpu_has_feature(CPU_FTR_ARCH_300)) { - pr_devel("DNCI: VCPU ID too high\n"); - goto out; - } - err = -ENOMEM; vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL); if (!vcpu) @@ -2055,8 +2049,13 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm, vcore = NULL; err = -EINVAL; if (cpu_has_feature(CPU_FTR_ARCH_300)) { - BUG_ON(kvm->arch.smt_mode != 1); - core = kvmppc_pack_vcpu_id(kvm, id); + if (id >= (KVM_MAX_VCPUS * kvm->arch.emul_smt_mode)) { + pr_devel("KVM: VCPU ID too high\n"); + core = KVM_MAX_VCORES; + } else { + BUG_ON(kvm->arch.smt_mode != 1); + core = kvmppc_pack_vcpu_id(kvm, id); + } } else { core = id / kvm->arch.smt_mode; } -- 2.7.4