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=-9.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 0F67FC10DCE for ; Sun, 15 Mar 2020 04:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C047B206E9 for ; Sun, 15 Mar 2020 04:10:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="n+liN5FZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726272AbgCOEKT (ORCPT ); Sun, 15 Mar 2020 00:10:19 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:38925 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbgCOEKT (ORCPT ); Sun, 15 Mar 2020 00:10:19 -0400 Received: by mail-wm1-f66.google.com with SMTP id f7so14380797wml.4; Sat, 14 Mar 2020 21:10:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id; bh=7NszvAXb9CGNqwT7dYeN3INhVSTlKBvqRmiaZIGgUzM=; b=n+liN5FZupOzuGmaL8W0VktGX+braNF2HwHqE4seR4kZiiex5TQZtj04W8EtxZmx4U N7mE03CKIQLzpncNE7yyQ09H6quoTKYstglmWXP3LhUtIZFh0jpumW8LqsW4n0aYNu5E 9Zsda/e4+bVvPPea+hDL96ZY/Un+MMEko9W15c6R4h0gGHl1FKReRQ+O/qaUHi4rpz31 mE8oVXifg5I+uCgDvF8+B0njfnmctgZY6IZAk4BeeTta8N+fg++CYNS1dtGmFiAHuhNJ h9ef3+9fGWIBNBEcI944HQfRxvk6l3tz04Tl6SJ4M+8dLIsYsa1ro7rfgL8rD96BGbKW EFTw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id; bh=7NszvAXb9CGNqwT7dYeN3INhVSTlKBvqRmiaZIGgUzM=; b=Tmlno+NuQnDfIWyxElYaw53OfcDweB5O4gV7uqc5XUONjouwFXkJKepnLOpXfHUweR 8Lf+0qmlovwbiCArmHdB8Dwl+NOdq1/V/HJMQdVeZ2FJ1KEeuTpQ1tnYBX3NsosQYCIW AT9ddpWDsLofJgLlkJTKQ99DPlMxnCz4/3X+QqQqhxPYLYTaQQk3IgYRxR5hXIYtnv/g ND1/QijKCNmT7699V512yMe8jz5HS/Jo63NFNXGcsQFB7naOKIpQyJr3OdDNLOO8AZql Xj251NdVHoSaPqc2zoD0KEXSJMu+ahoY1SZjfyYvPnI5wcitSRfnjTJFswQWxm36l9GC Okzw== X-Gm-Message-State: ANhLgQ0M4z43tTly+GEgvbFRzY4e8i4c5wXJmhxBhXwJmwob8HCyUkuo v9NlcWsMox4bHAEMOBdDBDiQCZp+ X-Google-Smtp-Source: ADFU+vttRMhC6z4KeEiI90Sln9kvzZ3oD5DpV2H2KhdjIUk7TSHX42UtdII4c1he6JrDUQ6cxbKKBQ== X-Received: by 2002:a7b:cb17:: with SMTP id u23mr16873136wmj.12.1584185482872; Sat, 14 Mar 2020 04:31:22 -0700 (PDT) Received: from 640k.localdomain ([93.56.174.5]) by smtp.gmail.com with ESMTPSA id n186sm454515wme.25.2020.03.14.04.31.21 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 14 Mar 2020 04:31:22 -0700 (PDT) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: linmiaohe@huawei.com, vkuznets@redhat.com Subject: [PATCH] KVM: X86: correct meaningless kvm_apicv_activated() check Date: Sat, 14 Mar 2020 12:31:20 +0100 Message-Id: <1584185480-3556-1-git-send-email-pbonzini@redhat.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org After test_and_set_bit() for kvm->arch.apicv_inhibit_reasons, we will always get false when calling kvm_apicv_activated() because it's sure apicv_inhibit_reasons do not equal to 0. What the code wants to do, is check whether APICv was *already* active and if so skip the costly request; we can do this using cmpxchg. Reported-by: Miaohe Lin Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a7cb85231330..49efa4529662 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8049,19 +8049,26 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu) */ void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit) { + unsigned long old, new, expected; + if (!kvm_x86_ops->check_apicv_inhibit_reasons || !kvm_x86_ops->check_apicv_inhibit_reasons(bit)) return; - if (activate) { - if (!test_and_clear_bit(bit, &kvm->arch.apicv_inhibit_reasons) || - !kvm_apicv_activated(kvm)) - return; - } else { - if (test_and_set_bit(bit, &kvm->arch.apicv_inhibit_reasons) || - kvm_apicv_activated(kvm)) - return; - } + old = READ_ONCE(kvm->arch.apicv_inhibit_reasons); + do { + expected = new = old; + if (activate) + __clear_bit(bit, &new); + else + __set_bit(bit, &new); + if (new == old) + break; + old = cmpxchg(&kvm->arch.apicv_inhibit_reasons, expected, new); + } while (old != expected); + + if ((old == 0) == (new == 0)) + return; trace_kvm_apicv_update_request(activate, bit); if (kvm_x86_ops->pre_update_apicv_exec_ctrl) -- 1.8.3.1