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=-5.3 required=3.0 tests=BAYES_00, 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 AAEA4C47095 for ; Wed, 9 Jun 2021 04:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7947F61351 for ; Wed, 9 Jun 2021 04:40:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235792AbhFIEmr (ORCPT ); Wed, 9 Jun 2021 00:42:47 -0400 Received: from mga03.intel.com ([134.134.136.65]:50937 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231335AbhFIEmq (ORCPT ); Wed, 9 Jun 2021 00:42:46 -0400 IronPort-SDR: oX5rPxONy4qSXk4ezTPzeGTiToeeKg2BI/nCGZ+yf6UyQRKmgCQHusi8NNyjpHrr6GshpQ7TYo XztH+QuOAx9w== X-IronPort-AV: E=McAfee;i="6200,9189,10009"; a="205027067" X-IronPort-AV: E=Sophos;i="5.83,260,1616482800"; d="scan'208";a="205027067" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Jun 2021 21:40:43 -0700 IronPort-SDR: CnHLeEBhcNgz2NyLL/DSIPWtc/cAx1WpIR7s09DMJ39lwswXLqZpARCXvJRTDwPxNXCVdqXheD jpN3aeGE56UQ== X-IronPort-AV: E=Sophos;i="5.83,260,1616482800"; d="scan'208";a="551856239" Received: from akleen-mobl1.amr.corp.intel.com (HELO [10.209.24.11]) ([10.209.24.11]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Jun 2021 21:40:43 -0700 Subject: Re: [RFC v2-fix-v4 1/1] x86/tdx: Skip WBINVD instruction for TDX guest To: Andy Lutomirski , "Williams, Dan J" , Sathyanarayanan Kuppuswamy Cc: "Peter Zijlstra (Intel)" , Dave Hansen , Tony Luck , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Raj Ashok , Sean Christopherson , Linux Kernel Mailing List References: <20210609011030.751451-1-sathyanarayanan.kuppuswamy@linux.intel.com> <23418f34-7c03-7477-6fbf-1b36b4718cb9@kernel.org> <4e5ac34f-28cb-def6-0b87-e560fa42e5e5@linux.intel.com> From: Andi Kleen Message-ID: <390d6712-35b5-e52a-fb32-205844bad4ef@linux.intel.com> Date: Tue, 8 Jun 2021 21:40:42 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> KVM only turns it into a noop if there is no VT-d, because with VT-d you >> might need it to turn mappings into uncached and vice versa. > Wow, I found the kvm_arch_register_noncoherent_dma() stuff. That's horrifying. What's it for? e e.g. if you want to run a GPU it really needs some uncached memory. Same is true for other more complex devices. Now modern Linux of course will be preferring CLFLUSH instead for the conversion, but there are old versions that preferred WBINVD. I don't think it's a DoS, as long as you're not too picky about latencies on the host. -Andi