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=-6.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 95622C432C0 for ; Tue, 19 Nov 2019 07:01:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5EE54208CC for ; Tue, 19 Nov 2019 07:01:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ft+p6Pvx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726994AbfKSHBz (ORCPT ); Tue, 19 Nov 2019 02:01:55 -0500 Received: from mail-oi1-f195.google.com ([209.85.167.195]:43680 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725878AbfKSHBy (ORCPT ); Tue, 19 Nov 2019 02:01:54 -0500 Received: by mail-oi1-f195.google.com with SMTP id l20so17900402oie.10; Mon, 18 Nov 2019 23:01:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=qz77BFNx7Mzy/MD1o3YVo9rJMBCL9I3q5BZGdkzee6E=; b=ft+p6PvxpkSpqyVCfKBkwoJ9cWG+lIgZDlW4rBbYsNdr/my6ZIlaxRNhEawqAOx24E JU2bg5u8gnVxdGZmJlE0h2iYcEccL1YM5MAdvz1/30irCnM5CnWS/XvMC+igIQPIf9zD 3IG4Wy6Wrss1w+MARmW437uRb8gDXPKxtO9NQvDpEeuy1AGu/MhZvtrWq1tGb6d51+Ts KWOzkPl3VYVC7GPcfnYbxEP6036+OIugWfRvP1AmqUvppEGo20h+7rwiTCPgLC2jJ77I D0EmrbS9yKHXawP+2gtee8WPxFYiRZpDaIWu2E+EXu1Kjgahx/euS/f1iXMxf89iHBZE 1qmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=qz77BFNx7Mzy/MD1o3YVo9rJMBCL9I3q5BZGdkzee6E=; b=SlAAS7N1bzc9Gb/7ewXsSk3Xmn0FVy5piY82nbsIY6yjZ/+c0VDFu5S1bhFvXaY37h v7L3SnscZUumlxAYJ845S/DoeauwkGVACTbNm6o8azCwES4UNSEPZYsGe306TUQdsrlJ BSp4BNPjB2iFpFYlDpeF+HNVVGbEXsJQ7Q4avEcNwwj+yYGu+JIu/c5L/E4tTOSZQUtO qG83KlLkfDvx96N73afELmUfaudxTlPmDLYBeqTxnrmU6I5tWZTkFUFZzyolFZhvj2/V +QzSegIDsq2M9AVZLKHWO4vtRs94fDXOIpEHu7uETTlvxPwFpRnwcCk+D2MBJxAyMxqj BvRA== X-Gm-Message-State: APjAAAUPn3hgtkP/GB0FlPWKdTLI6SHe10xNgNOqDxXKd8+arqugNEna gNFzKL9pPiQgB+avdn5zJspzrdfTtXRDMdMOkCo= X-Google-Smtp-Source: APXvYqwmGoKh3uUy1mY1+Rk/+b0NiC55jQDs6tDgUT9OAyqEAabRDmNRZTUwg+81GMFFRf9NBZUqS3aOPzRCkh04aqQ= X-Received: by 2002:aca:5015:: with SMTP id e21mr2814500oib.174.1574146913825; Mon, 18 Nov 2019 23:01:53 -0800 (PST) MIME-Version: 1.0 References: <1571829384-5309-1-git-send-email-zhenzhong.duan@oracle.com> <1571829384-5309-4-git-send-email-zhenzhong.duan@oracle.com> In-Reply-To: <1571829384-5309-4-git-send-email-zhenzhong.duan@oracle.com> From: Wanpeng Li Date: Tue, 19 Nov 2019 15:01:45 +0800 Message-ID: Subject: Re: [PATCH v8 3/5] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks To: Zhenzhong Duan Cc: LKML , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "the arch/x86 maintainers" , Paolo Bonzini , Radim Krcmar , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Boris Ostrovsky , Juergen Gross , Peter Zijlstra , will@kernel.org, linux-hyperv@vger.kernel.org, kvm , mikelley@microsoft.com, "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Sasha Levin , Jonathan Corbet , "H. Peter Anvin" Content-Type: text/plain; charset="UTF-8" Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Wed, 23 Oct 2019 at 19:21, Zhenzhong Duan wrote: > > There are cases where a guest tries to switch spinlocks to bare metal > behavior (e.g. by setting "xen_nopvspin" on XEN platform and > "hv_nopvspin" on HYPER_V). > > That feature is missed on KVM, add a new parameter "nopvspin" to disable > PV spinlocks for KVM guest. > > The new 'nopvspin' parameter will also replace Xen and Hyper-V specific > parameters in future patches. > > Define variable nopvsin as global because it will be used in future > patches as above. > > Signed-off-by: Zhenzhong Duan > Reviewed-by: Vitaly Kuznetsov > Cc: Jonathan Corbet > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: "H. Peter Anvin" > Cc: Paolo Bonzini > Cc: Radim Krcmar > Cc: Sean Christopherson > Cc: Vitaly Kuznetsov > Cc: Wanpeng Li > Cc: Jim Mattson > Cc: Joerg Roedel > Cc: Peter Zijlstra > Cc: Will Deacon Reviewed-by: Wanpeng Li > --- > Documentation/admin-guide/kernel-parameters.txt | 5 ++++ > arch/x86/include/asm/qspinlock.h | 1 + > arch/x86/kernel/kvm.c | 39 ++++++++++++++++++++----- > kernel/locking/qspinlock.c | 7 +++++ > 4 files changed, 45 insertions(+), 7 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index a84a83f..bd49ed2 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5334,6 +5334,11 @@ > as generic guest with no PV drivers. Currently support > XEN HVM, KVM, HYPER_V and VMWARE guest. > > + nopvspin [X86,KVM] > + Disables the qspinlock slow path using PV optimizations > + which allow the hypervisor to 'idle' the guest on lock > + contention. > + > xirc2ps_cs= [NET,PCMCIA] > Format: > ,,,,,[,[,[,]]] > diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h > index 444d6fd..d86ab94 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo > extern void __pv_init_lock_hash(void); > extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock); > +extern bool nopvspin; > > #define queued_spin_unlock queued_spin_unlock > /** > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 6562886..9834737 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -825,18 +825,36 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) > */ > void __init kvm_spinlock_init(void) > { > - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ > - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > + /* > + * In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an > + * advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is > + * preferred over native qspinlock when vCPU is preempted. > + */ > + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { > + pr_info("PV spinlocks disabled, no host support\n"); > return; > + } > > + /* > + * Disable PV spinlocks and use native qspinlock when dedicated pCPUs > + * are available. > + */ > if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { > - static_branch_disable(&virt_spin_lock_key); > - return; > + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints\n"); > + goto out; > } > > - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ > - if (num_possible_cpus() == 1) > - return; > + if (num_possible_cpus() == 1) { > + pr_info("PV spinlocks disabled, single CPU\n"); > + goto out; > + } > + > + if (nopvspin) { > + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter\n"); > + goto out; > + } > + > + pr_info("PV spinlocks enabled\n"); > > __pv_init_lock_hash(); > pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; > @@ -849,6 +867,13 @@ void __init kvm_spinlock_init(void) > pv_ops.lock.vcpu_is_preempted = > PV_CALLEE_SAVE(__kvm_vcpu_is_preempted); > } > + /* > + * When PV spinlock is enabled which is preferred over > + * virt_spin_lock(), virt_spin_lock_key's value is meaningless. > + * Just disable it anyway. > + */ > +out: > + static_branch_disable(&virt_spin_lock_key); > } > > #endif /* CONFIG_PARAVIRT_SPINLOCKS */ > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 2473f10..75193d6 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) > #include "qspinlock_paravirt.h" > #include "qspinlock.c" > > +bool nopvspin __initdata; > +static __init int parse_nopvspin(char *arg) > +{ > + nopvspin = true; > + return 0; > +} > +early_param("nopvspin", parse_nopvspin); > #endif > -- > 1.8.3.1 >