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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 5E917C47082 for ; Tue, 8 Jun 2021 01:00:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 426D26108C for ; Tue, 8 Jun 2021 01:00:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231151AbhFHBCX (ORCPT ); Mon, 7 Jun 2021 21:02:23 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:29847 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230314AbhFHBCW (ORCPT ); Mon, 7 Jun 2021 21:02:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623114029; 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=l9Hxnp9TzX1Qa0LPCbDI+r/Swgm1W5T0HqpzgDaMsIM=; b=cJCSUgDFNaKbpGVyueCsW9AsPJ87rUUNJ2uMBjgxXT2QJvdiZBdYfxXHP3+/3p6nGYzEWg tmD9Sw/ctpoL8CGN2Jao+RWPj6m+4UmOTw2ch+nQomfNLK+jYu4/ul7/uLSGdM5FMIH/GF Uck9AV0RXzwXaKJm07iuCruZvckdEOY= Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-239-gzXCXNEsOVaR2e1Nlh-Y7A-1; Mon, 07 Jun 2021 21:00:28 -0400 X-MC-Unique: gzXCXNEsOVaR2e1Nlh-Y7A-1 Received: by mail-pg1-f197.google.com with SMTP id t10-20020a6564ca0000b02902205085fa58so11179389pgv.16 for ; Mon, 07 Jun 2021 18:00:28 -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-transfer-encoding :content-language; bh=l9Hxnp9TzX1Qa0LPCbDI+r/Swgm1W5T0HqpzgDaMsIM=; b=FZNtGCwrpnjpyE/jsqUHlCYf9YS/RVm1RIxyRUnBghJ+zOpma87OLhc6yXEmnElxQi 1KAAXMqil0OefZ+XF4+f7AKrQX/2aDImUWC8gsNgEwF8JovM3PHjR2J9ZUXnOsPfGIjh XwVb65x1ieHHbmJWj1JjvMMTip4Wx5zJyjCnpsrqhCeNk8SD0B6UwUBbkMc7GZ+El9LY IgYbNSSoE3kNtvJiNFB0YabDGc3hYBCd1Fngg75f9T26dNOFghmAdNV1NL2JVe6kIGGh /HVrB7Fe8HaW89Z0AIzVlzU2aIthQQ20myQxl/C7/Qoo6hnCLfCdf808kv+Q9OxW0PA8 bC6g== X-Gm-Message-State: AOAM5336118BXT6ZYatHlz4BHw02ML1lUTxYCMp0jFNes4b9gRlL88Z6 hRrcpUEuV1mIzCHm6dCGy7x1dWh5+Fm4jLcUHvUIV08GD6axbDEdl6ixWFlLM5OmtGOU9xegbui nHrQNcWC5vX5m X-Received: by 2002:a17:90a:db0f:: with SMTP id g15mr1973144pjv.156.1623114026999; Mon, 07 Jun 2021 18:00:26 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwYWbmdIHR4JeIkPyMKnrD47V0fE4/gLC34oE2C1BXzJ6Yk+6wQV2cQXaOEH+lTIww5tPr8Pg== X-Received: by 2002:a17:90a:db0f:: with SMTP id g15mr1973123pjv.156.1623114026742; Mon, 07 Jun 2021 18:00:26 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id w142sm9258485pff.154.2021.06.07.18.00.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Jun 2021 18:00:26 -0700 (PDT) Subject: Re: [RFC] /dev/ioasid uAPI proposal To: Jason Gunthorpe Cc: Alex Williamson , "Tian, Kevin" , Jean-Philippe Brucker , "Jiang, Dave" , "Raj, Ashok" , "kvm@vger.kernel.org" , Jonathan Corbet , Robin Murphy , LKML , "iommu@lists.linux-foundation.org" , David Gibson , Kirti Wankhede , David Woodhouse , Gerd Hoffmann References: <20210602120111.5e5bcf93.alex.williamson@redhat.com> <20210602180925.GH1002214@nvidia.com> <20210602130053.615db578.alex.williamson@redhat.com> <20210602195404.GI1002214@nvidia.com> <20210602143734.72fb4fa4.alex.williamson@redhat.com> <6a9426d7-ed55-e006-9c4c-6b7c78142e39@redhat.com> <20210603130927.GZ1002214@nvidia.com> <65614634-1db4-7119-1a90-64ba5c6e9042@redhat.com> <20210604115805.GG1002214@nvidia.com> <895671cc-5ef8-bc1a-734c-e9e2fdf03652@redhat.com> <20210607141424.GF1002214@nvidia.com> From: Jason Wang Message-ID: <1cf9651a-b8ee-11f1-1f70-db3492a76400@redhat.com> Date: Tue, 8 Jun 2021 09:00:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210607141424.GF1002214@nvidia.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org ÔÚ 2021/6/7 ÏÂÎç10:14, Jason Gunthorpe дµÀ: > On Mon, Jun 07, 2021 at 11:18:33AM +0800, Jason Wang wrote: > >> Note that no drivers call these things doesn't meant it was not >> supported by the spec. > Of course it does. If the spec doesn't define exactly when the driver > should call the cache flushes for no-snoop transactions then the > protocol doesn't support no-soop. Just to make sure we are in the same page. What I meant is, if the DMA behavior like (no-snoop) is device specific. There's no need to mandate a virtio general attributes. We can describe it per device. The devices implemented in the current spec does not use non-coherent DMA doesn't mean any future devices won't do that. The driver could choose to use transport (e.g PCI), platform (ACPI) or device specific (general virtio command) way to detect and flush cache when necessary. > > no-snoop is only used in very specific sequences of operations, like > certain GPU usages, because regaining coherence on x86 is incredibly > expensive. > > ie I wouldn't ever expect a NIC to use no-snoop because NIC's expect > packets to be processed by the CPU. For NIC yes. But virtio is more that just NIC. We've already supported GPU and crypto devices. In this case, no-snoop will be useful since the data is not necessarily expected to be processed by CPU. And a lot of other type of devices are being proposed. Thanks > > "non-coherent DMA" is some general euphemism that evokes images of > embedded platforms that don't have coherent DMA at all and have low > cost ways to regain coherence. This is not at all what we are talking > about here at all. > > Jason >