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=-23.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 8AFE4C433E6 for ; Fri, 5 Feb 2021 17:55:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47BC664DEE for ; Fri, 5 Feb 2021 17:55:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231909AbhBEQN2 (ORCPT ); Fri, 5 Feb 2021 11:13:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233510AbhBEQJL (ORCPT ); Fri, 5 Feb 2021 11:09:11 -0500 Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37ADBC061786 for ; Fri, 5 Feb 2021 09:50:54 -0800 (PST) Received: by mail-pl1-x634.google.com with SMTP id a16so3942125plh.8 for ; Fri, 05 Feb 2021 09:50:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=8LdcV8DMgciJSckP8og9DY1KpzD/dHjlqzcgElgAVXM=; b=o26e66MUJ9hLAu9jrOp/+vQ/wqpT3vSn+OAqARm2Dr9nuJ9x0cpajYYgM/JZwGijHM amM2qTGshvMv9EP2EC42ryZgdh7/NhUxkeSOEkF7SuoSyH8sbTij9rUcrPdB5wz/Go59 je0R+HE+os02G5T5NbJ8vNA7OHm6CemIB5WVstzjKJyXlmVYSrI5P6N5NKZm1kw2pFEi 9PtA/Qmue6lAc1/NLPbkCpEH+WoTL+jFiCE7Z4wO4goZKDqk7tjWs8fdfozVd7iwAgTx baE2v9c7cFtOI8MQp61kF5cqiNRqWYKVaM4ipyBiorzEX7V48JJeY7n6FsVLCCNVgS2h 4Rsw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=8LdcV8DMgciJSckP8og9DY1KpzD/dHjlqzcgElgAVXM=; b=FFUZmPwwrGqyZkTAjX/KB6ztsKVf9oc/tUd35FapeEnByICHQNw1l1IpzfeY/LQ4xR VN2DlIpZE8VkSpsCxXccdtJ+9wLaScoZOgVOvpHkUY2uXnD/JqGvsGs0bu/Zw155eo/1 7vEkQMGVS8Bl/Rc+j5M5YU6kHtkrL8hHWOS3ENiYhlZ5ZU7+kQXgDt+t0Go5oDeyxK8U 7fdehjOQe12KSZCKgl/8yOwUng6HNqAwgp+xQUrgvpYZvsaTvvuxaoCg5VWIUjYlQg9A ezb09Rnj2oF31tLevrNH9MJLtbnZJwYOhzK436D11HSLOFotQjNbv6Wh8BNnndnlw6aU jBiw== X-Gm-Message-State: AOAM530BGTubZokdfI37M0xJYoWvIkVEmpU6wThcS7/MwU14pU50kXsR QAQ+8Jj6vB8P9YhGTNHs7xW/LbQsRDyR9w== X-Google-Smtp-Source: ABdhPJydY9NVYsb//m4vDxJl8NxvAKpuf/tVRmc9bhQXb3Zbesg4vXCHY8g9SUEA5D1wt6hntua+NA== X-Received: by 2002:a17:90a:a084:: with SMTP id r4mr5138668pjp.190.1612547453595; Fri, 05 Feb 2021 09:50:53 -0800 (PST) Received: from google.com ([2620:15c:f:10:d169:a9f7:513:e5]) by smtp.gmail.com with ESMTPSA id a6sm9445934pfr.43.2021.02.05.09.50.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Feb 2021 09:50:52 -0800 (PST) Date: Fri, 5 Feb 2021 09:50:46 -0800 From: Sean Christopherson To: Yu Zhang Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org Subject: Re: [PATCH] KVM: x86/MMU: Do not check unsync status for root SP. Message-ID: References: <20210116002100.17339-1-yu.c.zhang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210116002100.17339-1-yu.c.zhang@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 16, 2021, Yu Zhang wrote: > In shadow page table, only leaf SPs may be marked as unsync. > And for non-leaf SPs, we use unsync_children to keep the number > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync > shall always be zero for the root SP, hence no need to check it. > > Signed-off-by: Yu Zhang > --- > arch/x86/kvm/mmu/mmu.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 6d16481a..1a6bb03 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3412,8 +3412,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) > * mmu_need_write_protect() describe what could go wrong if this > * requirement isn't satisfied. > */ > - if (!smp_load_acquire(&sp->unsync) && > - !smp_load_acquire(&sp->unsync_children)) > + if (!smp_load_acquire(&sp->unsync_children)) > return; > > spin_lock(&vcpu->kvm->mmu_lock); Looks good. To make this less scary and more obviously correct, maybe move the the WARN on !PG_LEVEL_4K into kvm_unsync_page() instead of having the WARN in its sole caller, and add a WARN in mmu_sync_children()? diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 86af58294272..bc8ee05bb3d3 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu, LIST_HEAD(invalid_list); bool flush = false; + /* + * Only 4k SPTEs can directly be made unsync, the root shadow page + * should never be unsyc'd. + */ + WARN_ON_ONCE(sp->unsync); + while (mmu_unsync_walk(parent, &pages)) { bool protected = false; @@ -2502,6 +2508,8 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page); static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) { + WARN_ON(sp->role.level != PG_LEVEL_4K); + trace_kvm_mmu_unsync_page(sp); ++vcpu->kvm->stat.mmu_unsync; sp->unsync = 1; @@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, if (sp->unsync) continue; - WARN_ON(sp->role.level != PG_LEVEL_4K); kvm_unsync_page(vcpu, sp); } @@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) * mmu_need_write_protect() describe what could go wrong if this * requirement isn't satisfied. */ - if (!smp_load_acquire(&sp->unsync) && - !smp_load_acquire(&sp->unsync_children)) + if (!smp_load_acquire(&sp->unsync_children)) return; write_lock(&vcpu->kvm->mmu_lock);