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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, 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 7582CC433E9 for ; Wed, 27 Jan 2021 13:00:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 365102079A for ; Wed, 27 Jan 2021 13:00:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S313907AbhAZWtR (ORCPT ); Tue, 26 Jan 2021 17:49:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726685AbhAZVHy (ORCPT ); Tue, 26 Jan 2021 16:07:54 -0500 Received: from mail-io1-xd30.google.com (mail-io1-xd30.google.com [IPv6:2607:f8b0:4864:20::d30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15B1BC061574 for ; Tue, 26 Jan 2021 13:07:14 -0800 (PST) Received: by mail-io1-xd30.google.com with SMTP id n2so36613196iom.7 for ; Tue, 26 Jan 2021 13:07:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=aXltbeb08aCLv/IaAmMXa5/LJl/de149+mTZ0cnXywo=; b=DsTWBbWHcrIG9y6GeohkpNGVKY+cFZ1VjRR4+ukLSPPSSIvvVs1zd4QvHjD4UN0lWH nD4q16OAQLiKH9et9QRK4zu/uv1tLgOBIrBJfFub+OHPmmlnZmvSiWDdZawBPgNDpSIM TsLGIAideJ0EZE5LST9CPrMpOkrWtN2QkxcEqXTeREBTyrsSDZxz+847TOiGQWfds03b MY1+sDF/Jgaojxj1VxlNtoKcdLEoNdF80VSuwJ9aUBmq1aEhtLXUuAYHdmiTcWUxLc3M htpO1EYRPZz85zGWO1mQ2jYL9fsRPBLJXVtucvbSzlQocRqSApgRghjEtJkvca4rWSFM 0Yag== 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=aXltbeb08aCLv/IaAmMXa5/LJl/de149+mTZ0cnXywo=; b=Al5ezDPbWzlebVYl9gR+DqdQfHRGxNIbpM+RD0bV8z5ei5eLrQwkGtHeA8PlTg4N4R xLT0x69bEXG99pumKnAjebrEM9jsSNz/O2LZt5WD9jbB2KuyIbwnwqgmmYNKqyIxYHUb zMEUAr8o0VJInR2G929TR51eVHPMjVNfSxU9cL8HGOGHuSa8OPVjWKW9ZwR1i/c6sM/5 gD8ZSSu/INQ0zYWFRYkXEdgdb7ot2t51ki5AvGha32dR9JwDJzc9dvkTID2+0WwXqwMl Z2/dnnIKobsD1AvPTVOx1FAomTsEzYt5dVjfU5XNgcXw4Q5iBh1wvVtUP5Dp9WN2jE/G BETQ== X-Gm-Message-State: AOAM533ski2GxYK4VifnHDfpI2xOcnMFNGbH/pSYHEs70u/YUAmHsneI N2rfIvw8ErQ6O2MhXXdtL2oVUYUKZA43QpF7//sYng== X-Google-Smtp-Source: ABdhPJzdqrymF1yVhInjyCzYnkPoM9IF6RHa4r+wjRngK3JafTpx6MY+C8nP6uxewMUQmitEdGAyvgQs1DUk4YUYgD8= X-Received: by 2002:a92:cbce:: with SMTP id s14mr1159461ilq.306.1611695233297; Tue, 26 Jan 2021 13:07:13 -0800 (PST) MIME-Version: 1.0 References: <20210112181041.356734-1-bgardon@google.com> <20210112181041.356734-20-bgardon@google.com> <14147680-740d-6e7f-e00d-aa7698fd2ba6@redhat.com> In-Reply-To: <14147680-740d-6e7f-e00d-aa7698fd2ba6@redhat.com> From: Ben Gardon Date: Tue, 26 Jan 2021 13:07:01 -0800 Message-ID: Subject: Re: [PATCH 19/24] kvm: x86/mmu: Protect tdp_mmu_pages with a lock To: Paolo Bonzini Cc: LKML , kvm , Peter Xu , Sean Christopherson , Peter Shier , Peter Feiner , Junaid Shahid , Jim Mattson , Yulei Zhang , Wanpeng Li , Vitaly Kuznetsov , Xiao Guangrong Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Jan 26, 2021 at 5:37 AM Paolo Bonzini wrote: > > On 12/01/21 19:10, Ben Gardon wrote: > > + * May be acquired under the MMU lock in read mode or non-overlapping > > + * with the MMU lock. > > + */ > > + spinlock_t tdp_mmu_pages_lock; > > Is this correct? My understanding is that: > > - you can take tdp_mmu_pages_lock from a shared MMU lock critical section > > - you don't need to take tdp_mmu_pages_lock from an exclusive MMU lock > critical section, because you can't be concurrent with a shared critical > section > > - but then, you can't take tdp_mmu_pages_lock outside the MMU lock, > because you could have > > write_lock(mmu_lock) > spin_lock(tdp_mmu_pages_lock) > do tdp_mmu_pages_lock stuff !!! do tdp_mmu_pages_lock stuff > write_unlock(mmu_lock) > spin_unlock(tdp_mmu_pages_lock) > You're absolutely right, that would cause a problem. I'll amend the comment to specify that the lock should only be held under the mmu lock in read mode. > Paolo >