From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=x21H=ZZ=lists.ozlabs.org=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@kernel.org>
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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED,
	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 34F5DC432C3
	for <linuxppc-dev@archiver.kernel.org>; Tue,  3 Dec 2019 05:05:29 +0000 (UTC)
Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by mail.kernel.org (Postfix) with ESMTPS id 8B17B206E0
	for <linuxppc-dev@archiver.kernel.org>; Tue,  3 Dec 2019 05:05:28 +0000 (UTC)
Authentication-Results: mail.kernel.org;
	dkim=fail reason="signature verification failed" (2048-bit key) header.d=ozlabs-ru.20150623.gappssmtp.com header.i=@ozlabs-ru.20150623.gappssmtp.com header.b="fRZlsUEK"
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B17B206E0
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ozlabs.ru
Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3])
	by lists.ozlabs.org (Postfix) with ESMTP id 47RqgB1qFNzDqVQ
	for <linuxppc-dev@archiver.kernel.org>; Tue,  3 Dec 2019 16:05:26 +1100 (AEDT)
Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized)
 smtp.mailfrom=ozlabs.ru (client-ip=2607:f8b0:4864:20::1043;
 helo=mail-pj1-x1043.google.com; envelope-from=aik@ozlabs.ru;
 receiver=<UNKNOWN>)
Authentication-Results: lists.ozlabs.org;
 dmarc=none (p=none dis=none) header.from=ozlabs.ru
Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key;
 unprotected) header.d=ozlabs-ru.20150623.gappssmtp.com
 header.i=@ozlabs-ru.20150623.gappssmtp.com header.b="fRZlsUEK"; 
 dkim-atps=neutral
Received: from mail-pj1-x1043.google.com (mail-pj1-x1043.google.com
 [IPv6:2607:f8b0:4864:20::1043])
 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
 key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256)
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 47RpmH27KWzDqRw
 for <linuxppc-dev@lists.ozlabs.org>; Tue,  3 Dec 2019 15:24:47 +1100 (AEDT)
Received: by mail-pj1-x1043.google.com with SMTP id g4so958438pjs.10
 for <linuxppc-dev@lists.ozlabs.org>; Mon, 02 Dec 2019 20:24:47 -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=+iD8qt10cwcl+Zcsb9BMw7NrGdk2excR5RtcTLqorng=;
 b=fRZlsUEKeesPhpBKwtBZ3hr6Eb3W7sHOi0Qp4DUzi/hnUk3HwLTAtWtYMjYCMfPcTu
 gXBPVFTqju6MwrkT9lB6XNgYoCoHYKtyzpmCbsnki+XlMkrd1hJJcCdjdIOk9FQHt9Xr
 vlYTtHN3fLQZYwpurHVbg6Rzo/dA7xmQ0p19sHFII7jDP0gEC4uWvg8ZyrLDVhtteDet
 SAitGE+Q7af2+IuluPuwIyoKJ6YJu0qc8qXiUwZcB9XC+eD8TXTuIhKphNENUo13trOu
 hxwyPSP+yLm1gsZo8Xu8A3QHxoD98KwE88mYy8Zrxro+txg1kRcM325+qU+0q508BQvA
 L/vQ==
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=+iD8qt10cwcl+Zcsb9BMw7NrGdk2excR5RtcTLqorng=;
 b=sOtht240HT7ddBrV56k06EsjuL0YEuyGuhJ1ogKfDEtL3R82AMsEdpwo+8SrdY/J+2
 9koEpQbxdqY/mko6nvtLG7P/J/TEV7cTtj+FRLUKROQgmZnGFsq/9rdBWduuc7YxraWJ
 cYV5A1goVngNr7kzsz7r6djQXdUvt4sJlr4jH9xSymaTweJRVHuzJrFJ/YbC/q0MwG1d
 CZkthY+OsYLWKS92qiR/lQihROYd5020M+NeQiN2u4lnupAutQrnLgyx2vevN4yHa2sD
 fWYohTFh1M6+8SiM4eB1SqQEkvQNIxP61PwQt03qm3TQxgalHOgBpQsUFVIvUaoCyI1Q
 YTUQ==
X-Gm-Message-State: APjAAAV74UT2VGh2gX+nQtemO72+5rplZa+NEGz8QzT86WzD7skEzcqi
 Mev30Rnhwm0gQ4YFJpL45PyaNA==
X-Google-Smtp-Source: APXvYqyQ9uGUgptAxHIcsMNtfijcK7Tl29cWW8S4VkvfWfDY3I9RkjgUHWpUi775jWhM2qvC7cP1iQ==
X-Received: by 2002:a17:902:a714:: with SMTP id
 w20mr2908080plq.162.1575347085100; 
 Mon, 02 Dec 2019 20:24:45 -0800 (PST)
Received: from [10.61.2.175] ([122.99.82.10])
 by smtp.gmail.com with ESMTPSA id c1sm1227509pfa.51.2019.12.02.20.24.39
 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128);
 Mon, 02 Dec 2019 20:24:44 -0800 (PST)
Subject: Re: [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page
 with the hypervisor.
To: Ram Pai <linuxram@us.ibm.com>
References: <1575269124-17885-1-git-send-email-linuxram@us.ibm.com>
 <1575269124-17885-2-git-send-email-linuxram@us.ibm.com>
 <f08ace25-fa94-990b-1b6d-a1c0f30d6348@ozlabs.ru>
 <20191203020850.GA12354@oc0525413822.ibm.com>
 <0b56ce3e-6c32-5f3b-e7cc-0d419a61d71d@ozlabs.ru>
 <20191203040509.GB12354@oc0525413822.ibm.com>
From: Alexey Kardashevskiy <aik@ozlabs.ru>
Autocrypt: addr=aik@ozlabs.ru; keydata=
 mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD
 EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV
 /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo
 PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR
 tfLAeVpslNfWCi5ybPlowLx6KJqOsI9R2a9o4qRXWGP7IwiMRAC3iiPyk9cknt8ee6EUIxI6
 t847eFaVKI/6WcxhszI0R6Cj+N4y+1rHfkGWYWupCiHwj9DjILW9iEAncVgQmkNPpUsZECLT
 WQzMuVSxjuXW4nJ6f4OFHqL2dU//qR+BM/eJ0TT3OnfLcPqfucGxubhT7n/CXUxEy+mvWwnm
 s9p4uqVpTfEuzQ0/bE6t7dZdPBua7eYox1AQnk8JQDwC3Rn9kZq2O7u5KuJP5MfludMmQevm
 pHYEMF4vZuIpWcOrrSctJfIIEyhDoDmR34bCXAZfNJ4p4H6TPqPh671uMQV82CfTxTrMhGFq
 8WYU2AH86FrVQfWoH09z1WqhlOm/KZhAV5FndwVjQJs1MRXD8QARAQABtCRBbGV4ZXkgS2Fy
 ZGFzaGV2c2tpeSA8YWlrQG96bGFicy5ydT6JAjgEEwECACIFAk+rT0sCGwMGCwkIBwMCBhUI
 AgkKCwQWAgMBAh4BAheAAAoJEIYTPdgrwSC5fAIP/0wf/oSYaCq9PhO0UP9zLSEz66SSZUf7
 AM9O1rau1lJpT8RoNa0hXFXIVbqPPKPZgorQV8SVmYRLr0oSmPnTiZC82x2dJGOR8x4E01gK
 TanY53J/Z6+CpYykqcIpOlGsytUTBA+AFOpdaFxnJ9a8p2wA586fhCZHVpV7W6EtUPH1SFTQ
 q5xvBmr3KkWGjz1FSLH4FeB70zP6uyuf/B2KPmdlPkyuoafl2UrU8LBADi/efc53PZUAREih
 sm3ch4AxaL4QIWOmlE93S+9nHZSRo9jgGXB1LzAiMRII3/2Leg7O4hBHZ9Nki8/fbDo5///+
 kD4L7UNbSUM/ACWHhd4m1zkzTbyRzvL8NAVQ3rckLOmju7Eu9whiPueGMi5sihy9VQKHmEOx
 OMEhxLRQbzj4ypRLS9a+oxk1BMMu9cd/TccNy0uwx2UUjDQw/cXw2rRWTRCxoKmUsQ+eNWEd
 iYLW6TCfl9CfHlT6A7Zmeqx2DCeFafqEd69DqR9A8W5rx6LQcl0iOlkNqJxxbbW3ddDsLU/Y
 r4cY20++WwOhSNghhtrroP+gouTOIrNE/tvG16jHs8nrYBZuc02nfX1/gd8eguNfVX/ZTHiR
 gHBWe40xBKwBEK2UeqSpeVTohYWGBkcd64naGtK9qHdo1zY1P55lHEc5Uhlk743PgAnOi27Q
 ns5zuQINBE+rT0sBEACnV6GBSm+25ACT+XAE0t6HHAwDy+UKfPNaQBNTTt31GIk5aXb2Kl/p
 AgwZhQFEjZwDbl9D/f2GtmUHWKcCmWsYd5M/6Ljnbp0Ti5/xi6FyfqnO+G/wD2VhGcKBId1X
 Em/B5y1kZVbzcGVjgD3HiRTqE63UPld45bgK2XVbi2+x8lFvzuFq56E3ZsJZ+WrXpArQXib2
 hzNFwQleq/KLBDOqTT7H+NpjPFR09Qzfa7wIU6pMNF2uFg5ihb+KatxgRDHg70+BzQfa6PPA
 o1xioKXW1eHeRGMmULM0Eweuvpc7/STD3K7EJ5bBq8svoXKuRxoWRkAp9Ll65KTUXgfS+c0x
 gkzJAn8aTG0z/oEJCKPJ08CtYQ5j7AgWJBIqG+PpYrEkhjzSn+DZ5Yl8r+JnZ2cJlYsUHAB9
 jwBnWmLCR3gfop65q84zLXRQKWkASRhBp4JK3IS2Zz7Nd/Sqsowwh8x+3/IUxVEIMaVoUaxk
 Wt8kx40h3VrnLTFRQwQChm/TBtXqVFIuv7/Mhvvcq11xnzKjm2FCnTvCh6T2wJw3de6kYjCO
 7wsaQ2y3i1Gkad45S0hzag/AuhQJbieowKecuI7WSeV8AOFVHmgfhKti8t4Ff758Z0tw5Fpc
 BFDngh6Lty9yR/fKrbkkp6ux1gJ2QncwK1v5kFks82Cgj+DSXK6GUQARAQABiQIfBBgBAgAJ
 BQJPq09LAhsMAAoJEIYTPdgrwSC5NYEP/2DmcEa7K9A+BT2+G5GXaaiFa098DeDrnjmRvumJ
 BhA1UdZRdfqICBADmKHlJjj2xYo387sZpS6ABbhrFxM6s37g/pGPvFUFn49C47SqkoGcbeDz
 Ha7JHyYUC+Tz1dpB8EQDh5xHMXj7t59mRDgsZ2uVBKtXj2ZkbizSHlyoeCfs1gZKQgQE8Ffc
 F8eWKoqAQtn3j4nE3RXbxzTJJfExjFB53vy2wV48fUBdyoXKwE85fiPglQ8bU++0XdOr9oyy
 j1llZlB9t3tKVv401JAdX8EN0++ETiOovQdzE1m+6ioDCtKEx84ObZJM0yGSEGEanrWjiwsa
 nzeK0pJQM9EwoEYi8TBGhHC9ksaAAQipSH7F2OHSYIlYtd91QoiemgclZcSgrxKSJhyFhmLr
 QEiEILTKn/pqJfhHU/7R7UtlDAmFMUp7ByywB4JLcyD10lTmrEJ0iyRRTVfDrfVP82aMBXgF
 tKQaCxcmLCaEtrSrYGzd1sSPwJne9ssfq0SE/LM1J7VdCjm6OWV33SwKrfd6rOtvOzgadrG6
 3bgUVBw+bsXhWDd8tvuCXmdY4bnUblxF2B6GOwSY43v6suugBttIyW5Bl2tXSTwP+zQisOJo
 +dpVG2pRr39h+buHB3NY83NEPXm1kUOhduJUA17XUY6QQCAaN4sdwPqHq938S3EmtVhsuQIN
 BFq54uIBEACtPWrRdrvqfwQF+KMieDAMGdWKGSYSfoEGGJ+iNR8v255IyCMkty+yaHafvzpl
 PFtBQ/D7Fjv+PoHdFq1BnNTk8u2ngfbre9wd9MvTDsyP/TmpF0wyyTXhhtYvE267Av4X/BQT
 lT9IXKyAf1fP4BGYdTNgQZmAjrRsVUW0j6gFDrN0rq2J9emkGIPvt9rQt6xGzrd6aXonbg5V
 j6Uac1F42ESOZkIh5cN6cgnGdqAQb8CgLK92Yc8eiCVCH3cGowtzQ2m6U32qf30cBWmzfSH0
 HeYmTP9+5L8qSTA9s3z0228vlaY0cFGcXjdodBeVbhqQYseMF9FXiEyRs28uHAJEyvVZwI49
 CnAgVV/n1eZa5qOBpBL+ZSURm8Ii0vgfvGSijPGbvc32UAeAmBWISm7QOmc6sWa1tobCiVmY
 SNzj5MCNk8z4cddoKIc7Wt197+X/X5JPUF5nQRvg3SEHvfjkS4uEst9GwQBpsbQYH9MYWq2P
 PdxZ+xQE6v7cNB/pGGyXqKjYCm6v70JOzJFmheuUq0Ljnfhfs15DmZaLCGSMC0Amr+rtefpA
 y9FO5KaARgdhVjP2svc1F9KmTUGinSfuFm3quadGcQbJw+lJNYIfM7PMS9fftq6vCUBoGu3L
 j4xlgA/uQl/LPneu9mcvit8JqcWGS3fO+YeagUOon1TRqQARAQABiQRsBBgBCAAgFiEEZSrP
 ibrORRTHQ99dhhM92CvBILkFAlq54uICGwICQAkQhhM92CvBILnBdCAEGQEIAB0WIQQIhvWx
 rCU+BGX+nH3N7sq0YorTbQUCWrni4gAKCRDN7sq0YorTbVVSD/9V1xkVFyUCZfWlRuryBRZm
 S4GVaNtiV2nfUfcThQBfF0sSW/aFkLP6y+35wlOGJE65Riw1C2Ca9WQYk0xKvcZrmuYkK3DZ
 0M9/Ikkj5/2v0vxz5Z5w/9+IaCrnk7pTnHZuZqOh23NeVZGBls/IDIvvLEjpD5UYicH0wxv+
 X6cl1RoP2Kiyvenf0cS73O22qSEw0Qb9SId8wh0+ClWet2E7hkjWFkQfgJ3hujR/JtwDT/8h
 3oCZFR0KuMPHRDsCepaqb/k7VSGTLBjVDOmr6/C9FHSjq0WrVB9LGOkdnr/xcISDZcMIpbRm
 EkIQ91LkT/HYIImL33ynPB0SmA+1TyMgOMZ4bakFCEn1vxB8Ir8qx5O0lHMOiWMJAp/PAZB2
 r4XSSHNlXUaWUg1w3SG2CQKMFX7vzA31ZeEiWO8tj/c2ZjQmYjTLlfDK04WpOy1vTeP45LG2
 wwtMA1pKvQ9UdbYbovz92oyZXHq81+k5Fj/YA1y2PI4MdHO4QobzgREoPGDkn6QlbJUBf4To
 pEbIGgW5LRPLuFlOPWHmIS/sdXDrllPc29aX2P7zdD/ivHABslHmt7vN3QY+hG0xgsCO1JG5
 pLORF2N5XpM95zxkZqvYfC5tS/qhKyMcn1kC0fcRySVVeR3tUkU8/caCqxOqeMe2B6yTiU1P
 aNDq25qYFLeYxg67D/4w/P6BvNxNxk8hx6oQ10TOlnmeWp1q0cuutccblU3ryRFLDJSngTEu
 ZgnOt5dUFuOZxmMkqXGPHP1iOb+YDznHmC0FYZFG2KAc9pO0WuO7uT70lL6larTQrEneTDxQ
 CMQLP3qAJ/2aBH6SzHIQ7sfbsxy/63jAiHiT3cOaxAKsWkoV2HQpnmPOJ9u02TPjYmdpeIfa
 X2tXyeBixa3i/6dWJ4nIp3vGQicQkut1YBwR7dJq67/FCV3Mlj94jI0myHT5PIrCS2S8LtWX
 ikTJSxWUKmh7OP5mrqhwNe0ezgGiWxxvyNwThOHc5JvpzJLd32VDFilbxgu4Hhnf6LcgZJ2c
 Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V
 ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0
 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ
 DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T
 XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg==
Message-ID: <a0f19e65-81eb-37bd-928b-7a57a8660e3d@ozlabs.ru>
Date: Tue, 3 Dec 2019 15:24:37 +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: <20191203040509.GB12354@oc0525413822.ibm.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-BeenThere: linuxppc-dev@lists.ozlabs.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>
Cc: andmike@us.ibm.com, mst@redhat.com, mdroth@linux.vnet.ibm.com,
 linux-kernel@vger.kernel.org, ram.n.pai@gmail.com, cai@lca.pw,
 tglx@linutronix.de, sukadev@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
 hch@lst.de, bauerman@linux.ibm.com, david@gibson.dropbear.id.au
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>



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.


> 
>>
>>> This happens even
>>> on a normal VM when IOMMU is enabled.
>>>
>>>
>>>>
>>>> Also what is this for anyway? 
>>>
>>> This is for sending indirect-TCE entries to the hypervisor.
>>> The hypervisor must be able to read those TCE entries, so that it can 
>>> use those entires to populate the TCE table with the correct mappings.
>>>
>>>> if I understand things right, you cannot
>>>> map any random guest memory, you should only be mapping that 64MB-ish
>>>> bounce buffer array but 1) I do not see that happening (I may have
>>>> missed it) 2) it should be done once and it takes a little time for
>>>> whatever memory size we allow for bounce buffers anyway. Thanks,
>>>
>>> Any random guest memory can be shared by the guest. 
>>
>> Yes but we do not want this to be this random. 
> 
> It is not sharing some random page. It is sharing a page that is
> ear-marked for communicating TCE entries. Yes the address of the page
> can be random, depending on where the allocator decides to allocate it.
> The purpose of the page is not random.

I was talking about the location.


> That page is used for one specific purpose; to communicate the TCE
> entries to the hypervisor.  
> 
>> I thought the whole idea
>> of swiotlb was to restrict the amount of shared memory to bare minimum,
>> what do I miss?
> 
> I think, you are making a incorrect connection between this patch and
> SWIOTLB.  This patch has nothing to do with SWIOTLB.

I can see this and this is the confusing part.


>>
>>> Maybe you are confusing this with the SWIOTLB bounce buffers used by
>>> PCI devices, to transfer data to the hypervisor?
>>
>> Is not this for pci+swiotlb? 
> 
> 
> No. This patch is NOT for PCI+SWIOTLB.  The SWIOTLB pages are a
> different set of pages allocated and earmarked for bounce buffering.
> 
> This patch is purely to help the hypervisor setup the TCE table, in the
> presence of a IOMMU.

Then the hypervisor should be able to access the guest pages mapped for
DMA and these pages should be made unsecure for this to work. Where/when
does this happen?


>> The cover letter suggests it is for
>> virtio-scsi-_pci_ with 	iommu_platform=on which makes it a
>> normal pci device just like emulated XHCI. Thanks,
> 
> Well, I guess, the cover letter is probably confusing. There are two
> patches, which togather enable virtio on secure guests, in the presence
> of IOMMU.
> 
> The second patch enables virtio in the presence of a IOMMU, to use
> DMA_ops+SWIOTLB infrastructure, to correctly navigate the I/O to virtio
> devices.

The second patch does nothing in relation to the problem being solved.


> However that by itself wont work if the TCE entires are not correctly
> setup in the TCE tables.  The first patch; i.e this patch, helps
> accomplish that.
>> Hope this clears up the confusion.





-- 
Alexey