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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D763C433F5 for ; Wed, 20 Oct 2021 19:02:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 276F461212 for ; Wed, 20 Oct 2021 19:02:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231433AbhJTTEN (ORCPT ); Wed, 20 Oct 2021 15:04:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231312AbhJTTEL (ORCPT ); Wed, 20 Oct 2021 15:04:11 -0400 Received: from mail-pl1-x62a.google.com (mail-pl1-x62a.google.com [IPv6:2607:f8b0:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4E49DC06161C for ; Wed, 20 Oct 2021 12:01:57 -0700 (PDT) Received: by mail-pl1-x62a.google.com with SMTP id n11so16809206plf.4 for ; Wed, 20 Oct 2021 12:01:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=DANx3HO6cgPisAl+CHhBZy+n2kHgp44pkICwDmul91Y=; b=T2NpTM70PleU3Fgawia08s/phmB4W9mNfejNL2ZIBKiqj1LnIfPkJ+ajkOUm4p8Y7R yJg0aSR2qHZf4XvVVbHhpfkkoD/wL+gJv6TazBaQGH9k1P9sdh7Pl231jNNfXqq0ruDH wZMWuKyi7HsMW1lnaT5GRWpsVhH2KQWmRxtNTe79CVhjYrTnfcdej/kOgHttUwopLFE3 f/XdT1INFEaMarLdmGz6fIQddAsdZo37xruTpsVsMwQhmW9Z6C4rkSQBfx2bKTBKEmYQ sCjar7V528p8iltu4Z7FeKclr2dmHxuvQ3iXKTSvd3/w+Om0wfpCOQ4/noJJP+52FLO7 B4Tw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=DANx3HO6cgPisAl+CHhBZy+n2kHgp44pkICwDmul91Y=; b=hSyVBruYdy+Zw2Lqn+SxDyQne1u0EztbY1jGIS0eA6y4Hc/4+qzbBu26Z007vHJzS4 vrglMI95QZWOjb9fYFrPP6xz7ry/HpkJXcOvVoVd7ZccuO9zkTgkZ49cqd7mqHOXCbYI nfiupDSVqmBu8s7PaX2vGFvVu1R5RTohN4XNVOHF/ACR3XX8ZUwsOcE+8KJiFUgIDJMj 1IRa/yX17bo76UsXRfM84K5eCIWra9TGHtZMuaGWzs9fyVPbL4pB/K5zY95Qu4W+0t9z yu/hhTjpWFDUfeaM0t+bIdLoCQbHzv0td0UReCPRjsrrIzEJ4zIttBorGFVyTJ/R0tzw KTmw== X-Gm-Message-State: AOAM530Jw2tkR/MUukuf9VhPmDBuNNJC/E23mv4wEu6zYEPbeGm4QZHx 92VgsqDsrOm7E0H5yQEZKssR6w== X-Google-Smtp-Source: ABdhPJxTtZlD3tik07e31gwxjRrXsiDg7LAunZboxgnl2JeTj/bjMYSpzdfqi37yk9rhQ+Oc4bfF5g== X-Received: by 2002:a17:903:230f:b0:13f:cca9:bf2f with SMTP id d15-20020a170903230f00b0013fcca9bf2fmr821720plh.51.1634756516653; Wed, 20 Oct 2021 12:01:56 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id j198sm3003802pgc.4.2021.10.20.12.01.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Oct 2021 12:01:55 -0700 (PDT) Date: Wed, 20 Oct 2021 19:01:51 +0000 From: Sean Christopherson To: "Maciej S. Szmigiero" Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Igor Mammedov , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Oct 20, 2021, Maciej S. Szmigiero wrote: > On 20.10.2021 00:24, Sean Christopherson wrote: > > E.g. the whole thing can be > > > > if (!kvm->arch.n_requested_mmu_pages && > > (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) { > > unsigned long nr_mmu_pages; > > > > if (change == KVM_MR_CREATE) { > > kvm->arch.n_memslots_pages += new->npages; > > } else { > > WARN_ON(kvm->arch.n_memslots_pages < old->npages); > > kvm->arch.n_memslots_pages -= old->npages; > > } > > > > nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages; > > nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000); > > The above line will set nr_mmu_pages to zero since KVM_PERMILLE_MMU_PAGES > is 20, so when integer-divided by 1000 will result in a multiplication > coefficient of zero. Ugh, math. And thus do_div() to avoid the whole 64-bit divide issue on 32-bit KVM. Bummer.