From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB9A0C432C0 for ; Wed, 27 Nov 2019 18:39:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2B6D207DD for ; Wed, 27 Nov 2019 18:39:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727071AbfK0SjW (ORCPT ); Wed, 27 Nov 2019 13:39:22 -0500 Received: from mga12.intel.com ([192.55.52.136]:14574 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726593AbfK0SjW (ORCPT ); Wed, 27 Nov 2019 13:39:22 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Nov 2019 10:39:11 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,250,1571727600"; d="scan'208";a="292144779" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by orsmga001.jf.intel.com with ESMTP; 27 Nov 2019 10:39:11 -0800 Date: Wed, 27 Nov 2019 10:39:11 -0800 From: Sean Christopherson To: Ben Gardon Cc: kvm@vger.kernel.org, Paolo Bonzini , Peter Feiner , Peter Shier , Junaid Shahid , Jim Mattson Subject: Re: [RFC PATCH 04/28] kvm: mmu: Update the lpages stat atomically Message-ID: <20191127183911.GD22227@linux.intel.com> References: <20190926231824.149014-1-bgardon@google.com> <20190926231824.149014-5-bgardon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190926231824.149014-5-bgardon@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Sep 26, 2019 at 04:18:00PM -0700, Ben Gardon wrote: > In order to pave the way for more concurrent MMU operations, updates to > VM-global stats need to be done atomically. Change updates to the lpages > stat to be atomic in preparation for the introduction of parallel page > fault handling. > > Signed-off-by: Ben Gardon > --- > arch/x86/kvm/mmu.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 1ecd6d51c0ee0..56587655aecb9 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -1532,7 +1532,7 @@ static bool __drop_large_spte(struct kvm *kvm, u64 *sptep) > WARN_ON(page_header(__pa(sptep))->role.level == > PT_PAGE_TABLE_LEVEL); > drop_spte(kvm, sptep); > - --kvm->stat.lpages; > + xadd(&kvm->stat.lpages, -1); Manually doing atomic operations without converting the variable itself to an atomic feels like a hack, e.g. lacks the compile time checks provided by the atomics framework. Tangentially related, should the members of struct kvm_vm_stat be forced to 64-bit variables to avoid theoretical wrapping on 32-bit KVM? > return true; > } > > @@ -2676,7 +2676,7 @@ static bool mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp, > if (is_last_spte(pte, sp->role.level)) { > drop_spte(kvm, spte); > if (is_large_pte(pte)) > - --kvm->stat.lpages; > + xadd(&kvm->stat.lpages, -1); > } else { > child = page_header(pte & PT64_BASE_ADDR_MASK); > drop_parent_pte(child, spte); > @@ -3134,7 +3134,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access, > pgprintk("%s: setting spte %llx\n", __func__, *sptep); > trace_kvm_mmu_set_spte(level, gfn, sptep); > if (!was_rmapped && is_large_pte(*sptep)) > - ++vcpu->kvm->stat.lpages; > + xadd(&vcpu->kvm->stat.lpages, 1); > > if (is_shadow_present_pte(*sptep)) { > if (!was_rmapped) { > -- > 2.23.0.444.g18eeb5a265-goog >