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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 CB25CC433F5 for ; Sat, 18 Sep 2021 03:06:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B069A60FED for ; Sat, 18 Sep 2021 03:06:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240952AbhIRDIO (ORCPT ); Fri, 17 Sep 2021 23:08:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240737AbhIRDIM (ORCPT ); Fri, 17 Sep 2021 23:08:12 -0400 Received: from mail-io1-xd2d.google.com (mail-io1-xd2d.google.com [IPv6:2607:f8b0:4864:20::d2d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A22CAC061574; Fri, 17 Sep 2021 20:06:49 -0700 (PDT) Received: by mail-io1-xd2d.google.com with SMTP id a22so14626182iok.12; Fri, 17 Sep 2021 20:06:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=hb162fjdA++svSx4bcbnGtUQwKzEphYjoPNAoQasXSA=; b=INpgMBhc5bCcLGpZkUxXimTTTPZHb+e4+zSL/F3aZtHgGGrApBKP0DfPrPIE89Oy4E duOBORRuMzpeS6feX5u+h+4Z9smVTIcdAUDKjJvEmEPxfoI00l4aDUlRM+74Pc6Stkfv tqfHX68p5shPPdEcemZ9k3J/EwZD/pXb15znXhCh+9x6NxTis6+3pxjyjNRz/JzfS4GA Ew7NsQz5SWIWgySrmkw9M7xSughZx4jyXDwg7/HOfY/NsEbE361XCG65z1XhSGqrKqWt OQiyxOr2aZb2O0YALne9S8+RS3CMvJsARDB5w2p2B6ZPHPz0VG+XPTFJll/Halh407n1 3u5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hb162fjdA++svSx4bcbnGtUQwKzEphYjoPNAoQasXSA=; b=lZGibVtRtQ8JD8yuhPW+gOJk1bzlR5MTPGm0vPoG4AXt/bEDM0BUM+zsrGHLnhS3FP +gSnszQrCG0bzwoRJtCKf6xmB8mRIxdI/S2nWMavoM/e4CIwNdvrVI6jhyOoEHPZbEM1 KP0CtAC2kWV4YBg/XhQMzeFoskRRRNG/E9xR7HR1NvEtpXScO2w5sEChot9YY9F/irxK xxtrCnclI2O5XGtZeCXETJLxo/ezkrH4GZ9hHsrYdS2keqgPvCqKZanCsJmL0ZMgHdcY ZtXf2XLIdBC2soTFKjBKuJoMCLP5ujglgHOIJpRxdK86Bn1v4clYCDhvOAAp+rM4chxB PnMw== X-Gm-Message-State: AOAM531X1o0HcI+lKhpFy+OMBMvH5xPD6NDJzChPfLivD7csd7d5m85j IdRfeX1YXF8pPn6OuAYwPdmpTZ88f2G5A/m4u7mFs8ehr2w= X-Google-Smtp-Source: ABdhPJxMum/J8WLj7vI4WPq0VOeL+So4h+kAIb0sxPJK4YIA0cNbVPigfPJqlI3FMSDSf5i2uPnTgSWBhb1+aZ38CpM= X-Received: by 2002:a02:6d59:: with SMTP id e25mr11412408jaf.68.1631934409043; Fri, 17 Sep 2021 20:06:49 -0700 (PDT) MIME-Version: 1.0 References: <20210824075524.3354-1-jiangshanlai@gmail.com> <20210824075524.3354-6-jiangshanlai@gmail.com> <2f32727a108a626b71ab63b61cee567853ef2fdf.camel@redhat.com> In-Reply-To: <2f32727a108a626b71ab63b61cee567853ef2fdf.camel@redhat.com> From: Lai Jiangshan Date: Sat, 18 Sep 2021 11:06:37 +0800 Message-ID: Subject: Re: [PATCH 5/7] KVM: X86: Don't unsync pagetables when speculative To: Maxim Levitsky Cc: LKML , Paolo Bonzini , Lai Jiangshan , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , "H. Peter Anvin" , kvm@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It is weird that I did not receive this email. On Mon, Sep 13, 2021 at 7:02 PM Maxim Levitsky wrote: > > On Tue, 2021-08-24 at 15:55 +0800, Lai Jiangshan wrote: > > From: Lai Jiangshan > > > > We'd better only unsync the pagetable when there just was a really > > write fault on a level-1 pagetable. > > > > Signed-off-by: Lai Jiangshan > > --- > > arch/x86/kvm/mmu/mmu.c | 6 +++++- > > arch/x86/kvm/mmu/mmu_internal.h | 3 ++- > > arch/x86/kvm/mmu/spte.c | 2 +- > > 3 files changed, 8 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index a165eb8713bc..e5932af6f11c 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -2600,7 +2600,8 @@ static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) > > * were marked unsync (or if there is no shadow page), -EPERM if the SPTE must > > * be write-protected. > > */ > > -int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync) > > +int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync, > > + bool speculative) > > { > > struct kvm_mmu_page *sp; > > bool locked = false; > > @@ -2626,6 +2627,9 @@ int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync) > > if (sp->unsync) > > continue; > > > > + if (speculative) > > + return -EEXIST; > > Woudn't it be better to ensure that callers set can_unsync = false when speculating? I don't want to change the current behavior of "can_unsync" For a gfn: case1: All sps for the gfn are synced case2: Some sps for the gfn are synced and the others are not case3: All sps for the gfn are not synced "!can_unsync" causes the function to return non-zero for all cases. "speculative" causes the function to return non-zero for case1,case2. I don't think it would be bug if the behavior of old "!can_unsync" is changed to the behavior of this new "speculative". But the meaning of "!can_unsync" has to be changed. !can_unsync: all sps for @gfn can't be unsync. (derived from current code) ==> !can_unsync: it should not do any unsync operation. I have sent the patch in V2 without any change. If the new meaning is preferred, I will respin the patch, or I will send it separately if no other patches in V2 need to be updated. > > Also if I understand correctly this is not fixing a bug, but an optimization? > It is not fixing any bugs. But it is weird to do unsync operation on sps when speculative which would cause future overhead with no reason. > Best regards, > Maxim Levitsky > > > > + > > /* > > * TDP MMU page faults require an additional spinlock as they > > * run with mmu_lock held for read, not write, and the unsync > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h > > index 658d8d228d43..f5d8be787993 100644 > > --- a/arch/x86/kvm/mmu/mmu_internal.h > > +++ b/arch/x86/kvm/mmu/mmu_internal.h > > @@ -116,7 +116,8 @@ static inline bool kvm_vcpu_ad_need_write_protect(struct kvm_vcpu *vcpu) > > kvm_x86_ops.cpu_dirty_log_size; > > } > > > > -int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync); > > +int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync, > > + bool speculative); > > > > void kvm_mmu_gfn_disallow_lpage(const struct kvm_memory_slot *slot, gfn_t gfn); > > void kvm_mmu_gfn_allow_lpage(const struct kvm_memory_slot *slot, gfn_t gfn); > > diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c > > index 3e97cdb13eb7..b68a580f3510 100644 > > --- a/arch/x86/kvm/mmu/spte.c > > +++ b/arch/x86/kvm/mmu/spte.c > > @@ -159,7 +159,7 @@ int make_spte(struct kvm_vcpu *vcpu, unsigned int pte_access, int level, > > * e.g. it's write-tracked (upper-level SPs) or has one or more > > * shadow pages and unsync'ing pages is not allowed. > > */ > > - if (mmu_try_to_unsync_pages(vcpu, gfn, can_unsync)) { > > + if (mmu_try_to_unsync_pages(vcpu, gfn, can_unsync, speculative)) { > > pgprintk("%s: found shadow page for %llx, marking ro\n", > > __func__, gfn); > > ret |= SET_SPTE_WRITE_PROTECTED_PT; > >