From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 2/2] KVM: x86: Optimize mmio spte zapping when creating/moving memslot Date: Tue, 12 Mar 2013 22:40:12 -0300 Message-ID: <20130313014012.GA21171@amt.cnet> References: <20130312174333.7f76148e.yoshikawa_takuya_b1@lab.ntt.co.jp> <20130312174530.489f793c.yoshikawa_takuya_b1@lab.ntt.co.jp> <20130312120622.GZ11223@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Takuya Yoshikawa , kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51698 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755407Ab3CMBmN (ORCPT ); Tue, 12 Mar 2013 21:42:13 -0400 Content-Disposition: inline In-Reply-To: <20130312120622.GZ11223@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Mar 12, 2013 at 02:06:22PM +0200, Gleb Natapov wrote: > On Tue, Mar 12, 2013 at 05:45:30PM +0900, Takuya Yoshikawa wrote: > > When we create or move a memory slot, we need to zap mmio sptes. > > Currently, zap_all() is used for this and this is causing two problems: > > - extra page faults after zapping mmu pages > > - long mmu_lock hold time during zapping mmu pages > > > > For the latter, Marcelo reported a disastrous mmu_lock hold time during > > hot-plug, which made the guest unresponsive for a long time. > > > > This patch takes a simple way to fix these problems: do not zap mmu > > pages unless they are marked mmio cached. On our test box, this took > > only 50us for the 4GB guest and we did not see ms of mmu_lock hold time > > any more. > > > > Note that we still need to do zap_all() for other cases. So another > > work is also needed: Xiao's work may be the one. > > > > Signed-off-by: Takuya Yoshikawa > > --- > > arch/x86/include/asm/kvm_host.h | 1 + > > arch/x86/kvm/mmu.c | 18 ++++++++++++++++++ > > arch/x86/kvm/x86.c | 2 +- > > 3 files changed, 20 insertions(+), 1 deletions(-) > > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > index b84310a..028b03f 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -768,6 +768,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, > > struct kvm_memory_slot *slot, > > gfn_t gfn_offset, unsigned long mask); > > void kvm_mmu_zap_all(struct kvm *kvm); > > +void kvm_mmu_zap_mmio_sptes(struct kvm *kvm); > > unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm); > > void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages); > > > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > > index de45ec1..c1a9b7b 100644 > > --- a/arch/x86/kvm/mmu.c > > +++ b/arch/x86/kvm/mmu.c > > @@ -4189,6 +4189,24 @@ restart: > > spin_unlock(&kvm->mmu_lock); > > } > > > > +void kvm_mmu_zap_mmio_sptes(struct kvm *kvm) > > +{ > > + struct kvm_mmu_page *sp, *node; > > + LIST_HEAD(invalid_list); > > + > > + spin_lock(&kvm->mmu_lock); > > +restart: > > + list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) { > > + if (!sp->mmio_cached) > > + continue; > > + if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list)) > > + goto restart; > > + } > > + > > + kvm_mmu_commit_zap_page(kvm, &invalid_list); > > + spin_unlock(&kvm->mmu_lock); > > +} > > + > > static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc) > > { > > struct kvm *kvm; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 35b4912..16b6df2 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -6969,7 +6969,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, > > * mmio sptes. > > */ > > if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) { > I wonder why check for KVM_MR_MOVE here. For KVM_MR_MOVE > kvm_mmu_zap_all() should be called and it is indeed called by the common code. Its per memslot, the common code flush: kvm_arch_flush_shadow_memslot(kvm, slot);