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 BA34AC433F5 for ; Thu, 21 Oct 2021 17:45:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A256D61362 for ; Thu, 21 Oct 2021 17:45:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232425AbhJURsA (ORCPT ); Thu, 21 Oct 2021 13:48:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:59876 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232296AbhJURrF (ORCPT ); Thu, 21 Oct 2021 13:47:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634838289; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1EZ4owsWiZMNv5daeu40VXnvf5cZ9TsE7Nppy1IiXJY=; b=RqSUmF1rc61xqv7ncKru/LGqKV68Rg6iKCGzJ19Uo4wISbTbzdYOeUr1Bt46fl/GHZqOjS svIUpmOF7LjqncDvmAPp/KypJ6hA6Fchl9lUuUNhgqkMpyf1nPMDAvUyZGKBlgaIN4pIUl dLKOzyoqinjqGjfJ+GsI79ZKq+G9iDY= Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-445-WExqq0voO5q0MeikR-y0dw-1; Thu, 21 Oct 2021 13:44:47 -0400 X-MC-Unique: WExqq0voO5q0MeikR-y0dw-1 Received: by mail-ed1-f71.google.com with SMTP id t18-20020a056402021200b003db9e6b0e57so1129295edv.10 for ; Thu, 21 Oct 2021 10:44:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=1EZ4owsWiZMNv5daeu40VXnvf5cZ9TsE7Nppy1IiXJY=; b=RDX0SNv2V8tHwZEJUNJbvjEOLNDikB7NF1P5JcAum4f2kEQU8tp/U7JUKxGuEv1qdo dEPgKMEvGotzjCjARtrDsow4V0lZtea7KgPynWQWm5Et+aYVSXjaYbZHTKY8lJDMrXZx eJ3cBzoWXgThLjOakBZbTAV7E9eix4Jp+fdONcyHGcJyvtR62btrM+Y2697huaGtrMsi FW1YWeQplQsUSgVaGpmncQPoqpK2GYfuR4MuMEW1Xe+Toe73G0yQrmi1Anh6x97LndgE rrIDhp6/x3gwq4sD5coda0kEz64CZsT4GNexAsYhwjJ64ne7GeSRGJ+cprI+j00ncwCT SElg== X-Gm-Message-State: AOAM532PPxnPUpXZ0fuNyxqoYXASrklu16W4bcoBHAX5CyLfrytkS27a mNjJMP6/guQbdq4OkStE6LQ8rfve1zFzdznMrPL5spfhOwxE5Q+6RLeX0kAZFejqpqzZsCNgz9V +7sWDEhqv3ZpkImuDy9fsmgug X-Received: by 2002:a17:906:c18c:: with SMTP id g12mr8997376ejz.458.1634838286726; Thu, 21 Oct 2021 10:44:46 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxzmn6F9sw1Bbc/Myp0RL4CO+uvgDZnkcI99MTmxM0wkTKs6gjRYNBkVSPdMzU3BAfpHd/8+Q== X-Received: by 2002:a17:906:c18c:: with SMTP id g12mr8997336ejz.458.1634838286507; Thu, 21 Oct 2021 10:44:46 -0700 (PDT) Received: from ?IPV6:2001:b07:6468:f312:63a7:c72e:ea0e:6045? ([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.gmail.com with ESMTPSA id p26sm3115926edu.57.2021.10.21.10.44.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Oct 2021 10:44:45 -0700 (PDT) Message-ID: <7d97ff98-96c5-7699-7b32-36651ebf173d@redhat.com> Date: Thu, 21 Oct 2021 19:44:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [PATCH 3/4] KVM: X86: Use smp_rmb() to pair with smp_wmb() in mmu_try_to_unsync_pages() Content-Language: en-US To: Lai Jiangshan , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Lai Jiangshan , Junaid Shahid , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" References: <20211019110154.4091-1-jiangshanlai@gmail.com> <20211019110154.4091-4-jiangshanlai@gmail.com> From: Paolo Bonzini In-Reply-To: <20211019110154.4091-4-jiangshanlai@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/10/21 13:01, Lai Jiangshan wrote: > From: Lai Jiangshan > > The commit 578e1c4db2213 ("kvm: x86: Avoid taking MMU lock in > kvm_mmu_sync_roots if no sync is needed") added smp_wmb() in > mmu_try_to_unsync_pages(), but the corresponding smp_load_acquire() > isn't used on the load of SPTE.W which is impossible since the load of > SPTE.W is performed in the CPU's pagetable walking. > > This patch changes to use smp_rmb() instead. This patch fixes nothing > but just comments since smp_rmb() is NOP and compiler barrier() is not > required since the load of SPTE.W is before VMEXIT. I think that even implicit loads during pagetable walking obey read-read ordering on x86, but this is clearer and it is necessary for patch 4. Paolo