From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: Avoid zapping mmio sptes twice for generation wraparound Date: Wed, 03 Jul 2013 10:57:35 +0200 Message-ID: <51D3E77F.2060805@redhat.com> References: <20130703171804.89d6cc2c.yoshikawa_takuya_b1@lab.ntt.co.jp> <51D3E093.3020408@redhat.com> <51D3E33D.1090704@linux.vnet.ibm.com> <51D3E5DC.5020902@linux.vnet.ibm.com> <20130703085310.GD18508@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Xiao Guangrong , Takuya Yoshikawa , kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:24839 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932285Ab3GCI5q (ORCPT ); Wed, 3 Jul 2013 04:57:46 -0400 In-Reply-To: <20130703085310.GD18508@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 03/07/2013 10:53, Gleb Natapov ha scritto: >>> > > Please wait a while. I can not understand it very clearly. >>> > > >>> > > This conditional check will cause caching a overflow value into mmio spte. >>> > > The simple case is that kvm adds new slots for many times, the mmio-gen is easily >>> > > more than MMIO_MAX_GEN. >>> > > >> > >> > Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to >> > the end of install_new_memslots(). >> > > Exactly. Why should we hide it in obscure functions? Because kvm_mmu_invalidate_mmio_sptes is an x86-specific function, and we already have a good arch API to hook into __kvm_set_memory_region. Another possible implementation is to cache the last memslot generation, check it in kvm_arch_prepare/commit_memory_region, and call kvm_mmu_invalidate_mmio_sptes if it changed. This would avoid the need to keep "((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE))" in sync between the two places. But I don't think it is a substantial improvement. Paolo