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=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9901BC433EF for ; Mon, 13 Sep 2021 22:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B80C610D2 for ; Mon, 13 Sep 2021 22:32:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244842AbhIMWdO (ORCPT ); Mon, 13 Sep 2021 18:33:14 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37687 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238281AbhIMWdM (ORCPT ); Mon, 13 Sep 2021 18:33:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631572315; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+pe8dfj+kOBWXRxJxkk96MAr31FNxCfZh5AoAgmpL0s=; b=AvGcAwm6kO1TbqQU1eMWmwNOe+X+/wkWdgfCvLZT8fAmmr6qb71g+SzsoBh0OSWfhs55Mm Tgv32zovq5uYU1M5a0GY+t+qRyuhxkUKTVkFKgwtfpuWt7p6kTVdpakEdHCj/9eejictSQ AeY1eXCkoHz1e/5erlPGV6NhPQPfqy8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-263-19kveWv6O4eHzsLcN6Q6gg-1; Mon, 13 Sep 2021 18:31:54 -0400 X-MC-Unique: 19kveWv6O4eHzsLcN6Q6gg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 155DE1006AA0; Mon, 13 Sep 2021 22:31:53 +0000 (UTC) Received: from starship (unknown [10.35.206.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 641B95C1D1; Mon, 13 Sep 2021 22:31:44 +0000 (UTC) Message-ID: <974f204f02daab3d4e8e02b74514d01f92aeb88a.camel@redhat.com> Subject: Re: [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before link it From: Maxim Levitsky To: Sean Christopherson Cc: Lai Jiangshan , linux-kernel@vger.kernel.org, Paolo Bonzini , Lai Jiangshan , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Marcelo Tosatti , Avi Kivity , kvm@vger.kernel.org Date: Tue, 14 Sep 2021 01:31:43 +0300 In-Reply-To: References: <20210824075524.3354-1-jiangshanlai@gmail.com> <20210824075524.3354-3-jiangshanlai@gmail.com> <0103c8b2cccea601bd3474f47d982b37e9536921.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2021-09-13 at 20:49 +0000, Sean Christopherson wrote: > On Mon, Sep 13, 2021, Maxim Levitsky wrote: > > On Thu, 2021-09-02 at 23:40 +0000, Sean Christopherson wrote: > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > > index 4853c033e6ce..03293cd3c7ae 100644 > > > --- a/arch/x86/kvm/mmu/mmu.c > > > +++ b/arch/x86/kvm/mmu/mmu.c > > > @@ -2143,8 +2143,10 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, > > > kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); > > > } > > > > > > - if (sp->unsync_children) > > > - kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); > > > + if (sp->unsync_children) { > > > + kvm_make_all_cpus_request(KVM_REQ_MMU_SYNC, vcpu); > > > > I don't know the KVM mmu well so I miss something here most likely, > > but why to switch to kvm_make_all_cpus_request? > > > > MMU is shared by all VCPUs, and the process of its syncing should also do > > remote TLB flushes when needed? > > > > Another thing I don't fully understand is why this patch is needed. If we > > link an SP which has unsync children, we raise KVM_REQ_MMU_SYNC, which I > > think means that *this* vCPU will sync the whole MMU on next guest entry, > > including these unsync child SPs. Could you explain this? > > Answering all three questions at once, the problem is that KVM links in a new SP > that points at unsync'd SPs _before_ servicing KVM_REQ_MMU_SYNC. While the vCPU > is guaranteed to service KVM_REQ_MMU_SYNC before entering the guest, that doesn't > hold true for other vCPUs. As a result, there's a window where a different vCPU > can consume the stale, unsync SP via the new SP. > Thank you, now I understand! Best regards, Maxim Levitsky