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=-15.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 AC5AFC4338F for ; Mon, 2 Aug 2021 19:05:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92AA4610FC for ; Mon, 2 Aug 2021 19:05:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231175AbhHBTFb (ORCPT ); Mon, 2 Aug 2021 15:05:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33958 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229755AbhHBTFa (ORCPT ); Mon, 2 Aug 2021 15:05:30 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6DF7C061760 for ; Mon, 2 Aug 2021 12:05:20 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id j1so26487965pjv.3 for ; Mon, 02 Aug 2021 12:05:20 -0700 (PDT) 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=wgfgMVxCPBQ0GIYZVwRvz6smg5/pTXTIka/+zBBpuZk=; b=RG3wQlQziA+GjMEr81FaBBAaGIIW8dPtnvEJ9EWW+U3G3ykNoUxbSQfGCTghxJ7qx5 QYm8bwpA/Hr2tZ7Noc+uAMCeCktweksMH1VyqPEMrrskx66UCoNCX/LJDzyN1uXixhX8 c65KywHQsOQFSgrSOA/fIBLcSLdPpPgGc1ZFsOqdBfcKSoSj3+BuL9KiE1r5KEF/+eSa bjVzu8Bu8F66mmRAJaVEj9OpIvLtSAQgpYyvZBjJj46HxsokfUSEUYyxn6H6ALCyeisN ccfxLzNePC8I9IgQsjx35VDbDogXXHEPlkZ3uF6DZquLH24KjTflmTI91hbQ/WmY0URI aK2g== 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=wgfgMVxCPBQ0GIYZVwRvz6smg5/pTXTIka/+zBBpuZk=; b=AEAP2tsNmDijAnDhB7D6ADHuCUjHFwClA5r6pTvrZcEZHkbjRfpOsFpJKTqjBvjjZ3 +TvSV9mRc8M0I2ODGy2UD03/0JakW6lF6+lxF4fCnQ6RSW0Cu4r0yZaE1H+iJydLnm3W pR3vXjWazfEm4KjhB+RCIHY8/8nIKqAAiGwx/YAWXuqTi348+lI/ySt08siCdaa+qVzN jhoT5cs56np3miq8hVBKS09yRW2+OBt9cf/qrenWiRlsVatWF3Enwbzz8rb/0JOqqsOM +2ribCR6yfTXnDKpHoe/CNtric36Lw/szO4l75OfKwWo2Cgu6avKA3REWQwu7EpTl6ty 82ew== X-Gm-Message-State: AOAM532gRyzOPKQwgnHXii8rupqIbkuBaLlj5K/eABZVczOTD0uGLdb5 c8dcypwQsDa6g9zYe9+MFVtQgQ== X-Google-Smtp-Source: ABdhPJy4lW5VvswSn/50aGr5nBPbX5BezfjcGcMRQmajbM/t5mzCcanvKADCE20jv86zq7xao538fA== X-Received: by 2002:a17:902:dad0:b029:12c:83ca:fdd4 with SMTP id q16-20020a170902dad0b029012c83cafdd4mr15265788plx.77.1627931120160; Mon, 02 Aug 2021 12:05:20 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id x19sm9439006pgk.37.2021.08.02.12.05.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Aug 2021 12:05:19 -0700 (PDT) Date: Mon, 2 Aug 2021 19:05:15 +0000 From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 2/2] KVM: Don't take mmu_lock for range invalidation unless necessary Message-ID: References: <20210727171808.1645060-1-pbonzini@redhat.com> <20210727171808.1645060-3-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210727171808.1645060-3-pbonzini@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 27, 2021, Paolo Bonzini wrote: > @@ -605,8 +597,13 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, > > /* > * .change_pte() must be surrounded by .invalidate_range_{start,end}(), > + * If mmu_notifier_count is zero, then start() didn't find a relevant > + * memslot and wasn't forced down the slow path; rechecking here is > + * unnecessary. Critiquing my own comment... Maybe elaborate on what's (not) being rechecked? And also clarify that rechecking the memslots on a false positive (due to a second invalidation) is not problematic? * If mmu_notifier_count is zero, then no in-progress invalidations, * including this one, found a relevant memslot at start(); rechecking * memslots here is unnecessary. Note, a false positive (count elevated * by a different invalidation) is sub-optimal but functionally ok. */ Thanks for doing the heavy lifting! > */ > WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count)); > + if (!kvm->mmu_notifier_count) > + return; > > kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); > }