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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 169B4C43603 for ; Wed, 4 Dec 2019 22:26:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C248320661 for ; Wed, 4 Dec 2019 22:26:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs-ru.20150623.gappssmtp.com header.i=@ozlabs-ru.20150623.gappssmtp.com header.b="uMS/NAAQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728464AbfLDW0W (ORCPT ); Wed, 4 Dec 2019 17:26:22 -0500 Received: from mail-pg1-f194.google.com ([209.85.215.194]:41283 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728071AbfLDW0W (ORCPT ); Wed, 4 Dec 2019 17:26:22 -0500 Received: by mail-pg1-f194.google.com with SMTP id x8so539848pgk.8 for ; Wed, 04 Dec 2019 14:26:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ozlabs-ru.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=WuS+epwtlykmkeLsdcdL+jgUGc7m71KuRzIwHTzO75U=; b=uMS/NAAQcVsPCZpzd51ky8GrMVlkWa8WVFzC8FoZdxq5FNcwlqEnjsrHPswlamOprW UvUTkdze6o+kq19ps1Og2ihLF9eI+p4dvHQTSzdWvVusFCHuSZXu74btoNi2GnT63t00 zOvxH8dvkmK5ov7BG8IbOiKQCkf/eMnbMqBJtNMinzdRyUrTuIkFKseDA9kkq/izCG8w aIPdVqFJM6gRmnQ06k1J1SMqtJKZv3BIw/vDUIGPQESKJqZFItYPD0cxm8OT6XCeVgKX CDUh8T8E3PtWgqyQ0DyF7jPlEM/jrkkeGm3ETrOmB0x6JSPDCj5iciDXtpnpdqcUOjz4 EEcw== 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:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=WuS+epwtlykmkeLsdcdL+jgUGc7m71KuRzIwHTzO75U=; b=tMHCMHoWJM4Yv8fxsiQxUM6xJG2DYFCq+KmVaFFyCS3TWa0eZVyQZ5WmDmJtZh8N+s pLZi38QzE7EHdzXp0U5nxRwzrAZJrGzplw/9as4aVKEMfxOemnob3WrV//aD5+t7/lPn qJ99Aey29qtQmNbGBhLfMKJot2BOyEjZSoAejsXfZVxO6Ohh5CEbC3VIXkb3PSAqtID6 a0OYrPY9K2F2n7i/OTagQVW8tRYEmBjI0eXGiyJqt0GYWUaPaSi63bprpbquNKrp/BRl 3zKvf1Czi+FzXULu2Y21GWONhRiJMpl3GF2P/w6OsuKrG7pU8LWsyCxisdwovlMO0i6q XEpw== X-Gm-Message-State: APjAAAUK7/bZsfQ15Z93TAqzcfbP3wTS0fVPi/7nIsmR6ZpBITMSwGgF ZaDyi8xnyElK5SvN2WNlKXCd7kcJf80= X-Google-Smtp-Source: APXvYqynl2RRnkwLmzKxlgHMHjXddBtPWQGOBV2CJG+0t0BsdTfOpBeuZ/mOgCFtitHewZHrjb2WxQ== X-Received: by 2002:a63:4a1a:: with SMTP id x26mr5523761pga.298.1575498381278; Wed, 04 Dec 2019 14:26:21 -0800 (PST) Received: from [10.61.2.175] ([122.99.82.10]) by smtp.gmail.com with ESMTPSA id o7sm10014067pfg.138.2019.12.04.14.26.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Dec 2019 14:26:20 -0800 (PST) Subject: Re: [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor. To: Ram Pai , David Gibson Cc: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@ozlabs.org, mdroth@linux.vnet.ibm.com, hch@lst.de, andmike@us.ibm.com, sukadev@linux.vnet.ibm.com, mst@redhat.com, ram.n.pai@gmail.com, cai@lca.pw, tglx@linutronix.de, bauerman@linux.ibm.com, linux-kernel@vger.kernel.org References: <20191203020850.GA12354@oc0525413822.ibm.com> <0b56ce3e-6c32-5f3b-e7cc-0d419a61d71d@ozlabs.ru> <20191203040509.GB12354@oc0525413822.ibm.com> <20191203165204.GA5079@oc0525413822.ibm.com> <3a17372a-fcee-efbf-0a05-282ffb1adc90@ozlabs.ru> <20191204004958.GB5063@oc0525413822.ibm.com> <5963ff32-2119-be7c-d1e5-63457888a73b@ozlabs.ru> <20191204033618.GA5031@umbus.fritz.box> <20191204204232.GE5063@oc0525413822.ibm.com> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV 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Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: Date: Thu, 5 Dec 2019 09:26:14 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191204204232.GE5063@oc0525413822.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/12/2019 07:42, Ram Pai wrote: > On Wed, Dec 04, 2019 at 02:36:18PM +1100, David Gibson wrote: >> On Wed, Dec 04, 2019 at 12:08:09PM +1100, Alexey Kardashevskiy wrote: >>> >>> >>> On 04/12/2019 11:49, Ram Pai wrote: >>>> On Wed, Dec 04, 2019 at 11:04:04AM +1100, Alexey Kardashevskiy wrote: >>>>> >>>>> >>>>> On 04/12/2019 03:52, Ram Pai wrote: >>>>>> On Tue, Dec 03, 2019 at 03:24:37PM +1100, Alexey Kardashevskiy wrote: >>>>>>> >>>>>>> >>>>>>> On 03/12/2019 15:05, Ram Pai wrote: >>>>>>>> On Tue, Dec 03, 2019 at 01:15:04PM +1100, Alexey Kardashevskiy wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> On 03/12/2019 13:08, Ram Pai wrote: >>>>>>>>>> On Tue, Dec 03, 2019 at 11:56:43AM +1100, Alexey Kardashevskiy wrote: >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> On 02/12/2019 17:45, Ram Pai wrote: >>>>>>>>>>>> H_PUT_TCE_INDIRECT hcall uses a page filled with TCE entries, as one of >>>>>>>>>>>> its parameters. One page is dedicated per cpu, for the lifetime of the >>>>>>>>>>>> kernel for this purpose. On secure VMs, contents of this page, when >>>>>>>>>>>> accessed by the hypervisor, retrieves encrypted TCE entries. Hypervisor >>>>>>>>>>>> needs to know the unencrypted entries, to update the TCE table >>>>>>>>>>>> accordingly. There is nothing secret or sensitive about these entries. >>>>>>>>>>>> Hence share the page with the hypervisor. >>>>>>>>>>> >>>>>>>>>>> This unsecures a page in the guest in a random place which creates an >>>>>>>>>>> additional attack surface which is hard to exploit indeed but >>>>>>>>>>> nevertheless it is there. >>>>>>>>>>> A safer option would be not to use the >>>>>>>>>>> hcall-multi-tce hyperrtas option (which translates FW_FEATURE_MULTITCE >>>>>>>>>>> in the guest). >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Hmm... How do we not use it? AFAICT hcall-multi-tce option gets invoked >>>>>>>>>> automatically when IOMMU option is enabled. >>>>>>>>> >>>>>>>>> It is advertised by QEMU but the guest does not have to use it. >>>>>>>> >>>>>>>> Are you suggesting that even normal-guest, not use hcall-multi-tce? >>>>>>>> or just secure-guest? >>>>>>> >>>>>>> >>>>>>> Just secure. >>>>>> >>>>>> hmm.. how are the TCE entries communicated to the hypervisor, if >>>>>> hcall-multi-tce is disabled? >>>>> >>>>> Via H_PUT_TCE which updates 1 entry at once (sets or clears). >>>>> hcall-multi-tce enables H_PUT_TCE_INDIRECT (512 entries at once) and >>>>> H_STUFF_TCE (clearing, up to 4bln at once? many), these are simply an >>>>> optimization. >>>> >>>> Do you still think, secure-VM should use H_PUT_TCE and not >>>> H_PUT_TCE_INDIRECT? And normal VM should use H_PUT_TCE_INDIRECT? >>>> Is there any advantage of special casing it for secure-VMs. >>> >>> >>> Reducing the amount of insecure memory at random location. >> >> The other approach we could use for that - which would still allow >> H_PUT_TCE_INDIRECT, would be to allocate the TCE buffer page from the >> same pool that we use for the bounce buffers. I assume there must >> already be some sort of allocator for that? > > The allocator for swiotlb is buried deep in the swiotlb code. It is > not exposed to the outside-swiotlb world. Will have to do major surgery > to expose it. > > I was thinking, maybe we share the page, finish the INDIRECT_TCE call, > and unshare the page. This will address Alexey's concern of having > shared pages at random location, and will also give me my performance > optimization. Alexey: ok? I really do not see the point. I really think we should to 1:1 mapping of swtiotlb buffers using the default 32bit window using H_PUT_TCE and this should be more than enough, I do not think the amount of code will be dramatically different compared to unsecuring and securing a page or using one of swtiotlb pages for this purpose. Thanks, -- Alexey