From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH 2/2] KVM: async_pf: mm->mm_users can not pin apf->mm Date: Tue, 22 Apr 2014 22:24:40 +0200 Message-ID: <5356D008.8040204@de.ibm.com> References: <20140421132601.GA13615@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Dominik Dingel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Oleg Nesterov , Avi Kivity , Gleb Natapov , Paolo Bonzini Return-path: In-Reply-To: <20140421132601.GA13615@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 21/04/14 15:26, Oleg Nesterov wrote: > get_user_pages(mm) is simply wrong if mm->mm_users == 0 and exit_mmap/etc > was already called (or is in progress), mm->mm_count can only pin mm->pgd > and mm_struct itself. > > Change kvm_setup_async_pf/async_pf_execute to inc/dec mm->mm_users. > > kvm_create_vm/kvm_destroy_vm play with ->mm_count too but this case looks > fine at first glance, it seems that this ->mm is only used to verify that > current->mm == kvm->mm. > > Signed-off-by: Oleg Nesterov This looks fine, from what I can tell. The old code has the problem mentioned in your patch description, so your version is probably better. > --- > virt/kvm/async_pf.c | 8 ++++---- > 1 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c > index 0ced4f3..cda703e 100644 > --- a/virt/kvm/async_pf.c > +++ b/virt/kvm/async_pf.c > @@ -99,7 +99,7 @@ static void async_pf_execute(struct work_struct *work) > if (waitqueue_active(&vcpu->wq)) > wake_up_interruptible(&vcpu->wq); > > - mmdrop(mm); > + mmput(mm); > kvm_put_kvm(vcpu->kvm); > } > > @@ -116,7 +116,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) > flush_work(&work->work); > #else > if (cancel_work_sync(&work->work)) { > - mmdrop(work->mm); > + mmput(work->mm); > kvm_put_kvm(vcpu->kvm); /* == work->vcpu->kvm */ > kmem_cache_free(async_pf_cache, work); > } > @@ -181,7 +181,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva, > work->addr = hva; > work->arch = *arch; > work->mm = current->mm; > - atomic_inc(&work->mm->mm_count); > + atomic_inc(&work->mm->mm_users); > kvm_get_kvm(work->vcpu->kvm); > > /* this can't really happen otherwise gfn_to_pfn_async > @@ -199,7 +199,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva, > return 1; > retry_sync: > kvm_put_kvm(work->vcpu->kvm); > - mmdrop(work->mm); > + mmput(work->mm); > kmem_cache_free(async_pf_cache, work); > return 0; > } >