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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A41B6C28EBD for ; Sun, 9 Jun 2019 09:37:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 796C8208E4 for ; Sun, 9 Jun 2019 09:37:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727982AbfFIJhX (ORCPT ); Sun, 9 Jun 2019 05:37:23 -0400 Received: from mail-wm1-f51.google.com ([209.85.128.51]:55126 "EHLO mail-wm1-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727720AbfFIJhX (ORCPT ); Sun, 9 Jun 2019 05:37:23 -0400 Received: by mail-wm1-f51.google.com with SMTP id g135so5804344wme.4 for ; Sun, 09 Jun 2019 02:37:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=N/JT6wxx8SnEUHFdFMXDjIDadpkBg6G764joNYPh7l8=; b=rfSsX6rFs3jNsZUnhny8bBYoLkvb3wn9pbFy7raGbWuKiZZY7rRTwIEHpY7cbI6haG QBP9xpjfKrDJU3Wtj3Cujj1R8TIfSZDujPg6YXbeUX+aYAM12nqMFDGYAoMvkyAa28eq grWf8osu0Wpdpz+vIu6qSB30OWmPHNvEqH9scN5Ll8+oSCDVxUwrbi3HCJrc/3RDkhU4 590jOBPhMu0gGc+WerZPIHz4v6UPCUztTB7wiVRcCgNLZksNvTiRfGM2hs26EeiCAbZB Sh8DMEwzL4w1kUEaNxeP2P3xs/aA/TGYKtJJgv73nSUZRDbt252zyJGVIefCruWld9bf nhlw== X-Gm-Message-State: APjAAAVmD+o6F0p9lTPWuEVKHrKWoifhPxTZD2nHjgSL3x+4p/0L3+s1 +TJhTPQT5cATlqixS+OHml/Akg== X-Google-Smtp-Source: APXvYqyAtJD90KBreJ8YMy512INUJXccvzCGcpA/XJQQf/F7Ze/ETljJlq57FHnss/Ayp0CtUHfiww== X-Received: by 2002:a1c:7d56:: with SMTP id y83mr9949310wmc.77.1560073041026; Sun, 09 Jun 2019 02:37:21 -0700 (PDT) Received: from ?IPv6:2001:b07:6468:f312:8cc3:8abd:4519:2cd6? ([2001:b07:6468:f312:8cc3:8abd:4519:2cd6]) by smtp.gmail.com with ESMTPSA id b5sm7097123wru.69.2019.06.09.02.37.20 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Sun, 09 Jun 2019 02:37:20 -0700 (PDT) Subject: Re: Reference count on pages held in secondary MMUs To: Christoffer Dall , kvm@vger.kernel.org Cc: aarcange@redhat.com, kvmarm@lists.cs.columbia.edu References: <20190609081805.GC21798@e113682-lin.lund.arm.com> From: Paolo Bonzini Message-ID: <3ca445bb-0f48-3e39-c371-dd197375c966@redhat.com> Date: Sun, 9 Jun 2019 11:37:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190609081805.GC21798@e113682-lin.lund.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 09/06/19 10:18, Christoffer Dall wrote: > In some sense, we are thus maintaining a 'hidden', or internal, > reference to the page, which is not counted anywhere. > > I am wondering if it would be equally valid to take a reference on the > page, and remove that reference when unmapping via MMU notifiers, and if > so, if there would be any advantages/drawbacks in doing so? If I understand correctly, I think the MMU notifier would not fire if you took an actual reference; the page would be pinned in memory and could not be swapped out. Paolo