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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 13 Feb 2020 14:48:18 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01DEmHk242926226 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 13 Feb 2020 14:48:17 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 24BE611C050; Thu, 13 Feb 2020 14:48:17 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7E80F11C04A; Thu, 13 Feb 2020 14:48:16 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.71]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 13 Feb 2020 14:48:16 +0000 (GMT) Subject: Re: [PATCH 01/35] mm:gup/writeback: add callbacks for inaccessible pages To: Will Deacon Cc: Janosch Frank , Andrew Morton , Marc Zyngier , Sean Christopherson , Tom Lendacky , KVM , Cornelia Huck , David Hildenbrand , Thomas Huth , Ulrich Weigand , Claudio Imbrenda , Andrea Arcangeli , linux-s390 , Michael Mueller , Vasily Gorbik , linux-mm@kvack.org, kvm-ppc@vger.kernel.org, Paolo Bonzini , mark.rutland@arm.com, qperret@google.com, palmerdabbelt@google.com References: <20200207113958.7320-1-borntraeger@de.ibm.com> <20200207113958.7320-2-borntraeger@de.ibm.com> <28792269-e053-ac70-a344-45612ee5c729@de.ibm.com> <20200211112611.GD8560@willie-the-truck> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200211112611.GD8560@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 20021314-4275-0000-0000-000003A126AC X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20021314-4276-0000-0000-000038B52836 Message-Id: <618384fa-fa5e-66e8-221a-726e7dcf1d8c@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-13_04:2020-02-12,2020-02-13 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 lowpriorityscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 spamscore=0 mlxscore=0 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002130115 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11.02.20 12:26, Will Deacon wrote: > On Mon, Feb 10, 2020 at 06:27:04PM +0100, Christian Borntraeger wrote: >> CC Marc Zyngier for KVM on ARM. Marc, see below. Will there be any >> use for this on KVM/ARM in the future? >=20 > I can't speak for Marc, but I can say that we're interested in somethin= g > like this for potentially isolating VMs from a KVM host in Android. > However, we've currently been working on the assumption that the memory > removed from the host won't usually be touched by the host (i.e. no > KSM or swapping out), so all we'd probably want at the moment is to be > able to return an error back from arch_make_page_accessible(). Its retu= rn > code is ignored in this patch :/ I think there are two ways at the moment. One is to keep the memory away = from Linux, e.g. by using the memory as device driver memory like kmalloc. Thi= s is kind of what Power does. And I understand you as you want to follow that = model and do not want to use paging, file backing or so. Our approach tries to fully integrate into the existing Linux LRU methods= . Back to your approach. What happens when a malicious QEMU would start dir= ect I/O on such isolated memory? Is that what you meant by adding error checking = in these hooks. For the gup.c code returning an error seems straightforward. I have no idea what to do in writeback. When somebody managed to trigger = writeback on such a page, it already seems too late.=20