From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754199AbdBQA3R (ORCPT ); Thu, 16 Feb 2017 19:29:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46300 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753186AbdBQA3Q (ORCPT ); Thu, 16 Feb 2017 19:29:16 -0500 From: Bandan Das To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 2/3] KVM: use separate generations for each address space References: <20170215220048.3423-1-pbonzini@redhat.com> <20170215220048.3423-3-pbonzini@redhat.com> Date: Thu, 16 Feb 2017 19:29:15 -0500 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 17 Feb 2017 00:29:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > This will make it easier to support multiple address spaces in > kvm_gfn_to_hva_cache_init. Instead of having to check the address > space id, we can keep on checking just the generation number. > > Signed-off-by: Paolo Bonzini > --- > virt/kvm/kvm_main.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index e21bac7ed5d3..a83c186cefc1 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void) > if (!slots) > return NULL; > > - /* > - * Init kvm generation close to the maximum to easily test the > - * code of handling generation number wrap-around. > - */ > - slots->generation = -150; > for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) > slots->id_to_index[i] = slots->memslots[i].id = i; > > @@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type) > > r = -ENOMEM; > for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { > - kvm->memslots[i] = kvm_alloc_memslots(); > - if (!kvm->memslots[i]) > + struct kvm_memslots *slots = kvm_alloc_memslots(); > + if (!slots) > goto out_err_no_srcu; > + /* > + * Generations must be different for each address space. > + * Init kvm generation close to the maximum to easily test the > + * code of handling generation number wrap-around. > + */ > + slots->generation = i * 2 - 150; > + rcu_assign_pointer(kvm->memslots[i], slots); > } I can't seem to understand why rcu_assign_pointer wasn't used before. kvm->memslots[i] was a rcu protected pointer even before this change, right ? > if (init_srcu_struct(&kvm->srcu)) > @@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, > * Increment the new memslot generation a second time. This prevents > * vm exits that race with memslot updates from caching a memslot > * generation that will (potentially) be valid forever. > + * > + * Generations must be unique even across address spaces. We do not need > + * a global counter for that, instead the generation space is evenly split > + * across address spaces. For example, with two address spaces, address > + * space 0 will use generations 0, 4, 8, ... while * address space 1 will > + * use generations 2, 6, 10, 14, ... > */ > - slots->generation++; > + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1; > > kvm_arch_memslots_updated(kvm, slots);