Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751923AbdG1G5p (ORCPT ); Fri, 28 Jul 2017 02:57:45 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:37741 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbdG1G5n (ORCPT ); Fri, 28 Jul 2017 02:57:43 -0400 Subject: Re: [PATCH] KVM: nVMX: do not pin the VMCS12 To: David Matlack Cc: "linux-kernel@vger.kernel.org" , kvm list , Jim Mattson , Christian Borntraeger References: <1501163686-13648-1-git-send-email-pbonzini@redhat.com> From: Paolo Bonzini Message-ID: <78593b07-5d67-ac7e-eb5b-fdefee2a3477@redhat.com> Date: Fri, 28 Jul 2017 08:57:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3703 Lines: 97 On 27/07/2017 19:20, David Matlack wrote: >> + kvm_vcpu_write_guest_page(&vmx->vcpu, >> + vmx->nested.current_vmptr >> PAGE_SHIFT, >> + vmx->nested.cached_vmcs12, 0, VMCS12_SIZE); > Have you hit any "suspicious RCU usage" error messages during VM > teardown with this patch? We did when we replaced memcpy with > kvm_write_guest a while back. IIRC it was due to kvm->srcu not being > held in one of the teardown paths. kvm_write_guest() expects it to be > held in order to access memslots. > > We fixed this by skipping the VMCS12 flush during VMXOFF. I'll send > that patch along with a few other nVMX dirty tracking related patches > I've been meaning to get upstreamed. Oh, right. I had this other (untested) patch in the queue after Christian recently annotated everything with RCU checks: Paolo diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 890b706d1943..07e3b02a1be3 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -477,7 +477,8 @@ struct kvm { static inline struct kvm_io_bus *kvm_get_bus(struct kvm *kvm, enum kvm_bus idx) { return srcu_dereference_check(kvm->buses[idx], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock)); + lockdep_is_held(&kvm->slots_lock) || + !refcount_read(&kvm->users_count)); } static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i) @@ -570,7 +571,8 @@ void kvm_put_kvm(struct kvm *kvm); static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock)); + lockdep_is_held(&kvm->slots_lock) || + !refcount_read(&kvm->users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f3f74271f1a9..6a21c98b22bf 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -655,7 +655,6 @@ static struct kvm *kvm_create_vm(unsigned long type) mutex_init(&kvm->lock); mutex_init(&kvm->irq_lock); mutex_init(&kvm->slots_lock); - refcount_set(&kvm->users_count, 1); INIT_LIST_HEAD(&kvm->devices); r = kvm_arch_init_vm(kvm, type); @@ -701,6 +700,7 @@ static struct kvm *kvm_create_vm(unsigned long type) if (r) goto out_err; + refcount_set(&kvm->users_count, 1); spin_lock(&kvm_lock); list_add(&kvm->vm_list, &vm_list); spin_unlock(&kvm_lock); @@ -717,10 +717,9 @@ static struct kvm *kvm_create_vm(unsigned long type) hardware_disable_all(); out_err_no_disable: for (i = 0; i < KVM_NR_BUSES; i++) - kfree(rcu_access_pointer(kvm->buses[i])); + kfree(kvm_get_bus(kvm, i)); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) - kvm_free_memslots(kvm, - rcu_dereference_protected(kvm->memslots[i], 1)); + kvm_free_memslots(kvm, __kvm_memslots(kvm, i)); kvm_arch_free_vm(kvm); mmdrop(current->mm); return ERR_PTR(r); @@ -754,9 +754,8 @@ static void kvm_destroy_vm(struct kvm *kvm) spin_unlock(&kvm_lock); kvm_free_irq_routing(kvm); for (i = 0; i < KVM_NR_BUSES; i++) { - struct kvm_io_bus *bus; + struct kvm_io_bus *bus = kvm_get_bus(kvm, i); - bus = rcu_dereference_protected(kvm->buses[i], 1); if (bus) kvm_io_bus_destroy(bus); kvm->buses[i] = NULL; @@ -770,8 +769,7 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_arch_destroy_vm(kvm); kvm_destroy_devices(kvm); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) - kvm_free_memslots(kvm, - rcu_dereference_protected(kvm->memslots[i], 1)); + kvm_free_memslots(kvm, __kvm_memslots(kvm, i)); cleanup_srcu_struct(&kvm->irq_srcu); cleanup_srcu_struct(&kvm->srcu); kvm_arch_free_vm(kvm);