From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2] KVM: MMU: Don't use RCU for lockless shadow walking Date: Tue, 24 Apr 2012 13:42:05 +0300 Message-ID: <4F96837D.2040808@redhat.com> References: <1335260845-16271-1-git-send-email-avi@redhat.com> <4F967CD1.1020605@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org To: Xiao Guangrong Return-path: Received: from mx1.redhat.com ([209.132.183.28]:15197 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751449Ab2DXKmI (ORCPT ); Tue, 24 Apr 2012 06:42:08 -0400 In-Reply-To: <4F967CD1.1020605@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 04/24/2012 01:13 PM, Xiao Guangrong wrote: > On 04/24/2012 05:47 PM, Avi Kivity wrote: > > > > static void kvm_mmu_commit_zap_page(struct kvm *kvm, > > struct list_head *invalid_list) > > { > > @@ -2021,17 +2006,17 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, > > if (list_empty(invalid_list)) > > return; > > > > - kvm_flush_remote_tlbs(kvm); > > - > > - if (atomic_read(&kvm->arch.reader_counter)) { > > - kvm_mmu_isolate_pages(invalid_list); > > - sp = list_first_entry(invalid_list, struct kvm_mmu_page, link); > > - list_del_init(invalid_list); > > + /* > > + * wmb: make sure everyone sees our modifications to the page tables > > > Other lockless vcpu can see a old-copy of a spte, but it is ok since all page > tables is valid to be used. (kvm_flush_remote_tlbs can stop page table to be > freed) We want kvm_commit_zap_page() to see the changes before freeing memory. But maybe it's the responsibility of kmem_cache_free()/kmem_cache_alloc(). > > + * rmb: make sure we see changes to vcpu->mode > > > It is the responsibility of kvm_flush_remote_tlbs to see changes to vcpu->mode. > No? Yes. -- error compiling committee.c: too many arguments to function