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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 10 Feb 2020 18:28:37 -0000 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01AISZ8Z51838998 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 10 Feb 2020 18:28:35 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9D1A35204F; Mon, 10 Feb 2020 18:28:35 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.7.195]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 58D105204E; Mon, 10 Feb 2020 18:28:34 +0000 (GMT) Subject: Re: [PATCH 01/35] mm:gup/writeback: add callbacks for inaccessible pages To: David Hildenbrand , Janosch Frank Cc: KVM , Cornelia Huck , Thomas Huth , Ulrich Weigand , Claudio Imbrenda , Andrea Arcangeli , linux-s390 , Michael Mueller , Vasily Gorbik , linux-mm@kvack.org, Andrew Morton , Michal Hocko References: <20200207113958.7320-1-borntraeger@de.ibm.com> <20200207113958.7320-2-borntraeger@de.ibm.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 20021018-0008-0000-0000-000003519A91 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20021018-0009-0000-0000-00004A72395C Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-10_06:2020-02-10,2020-02-10 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 phishscore=0 mlxlogscore=999 impostorscore=0 bulkscore=0 priorityscore=1501 adultscore=0 lowpriorityscore=0 spamscore=0 clxscore=1015 suspectscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002100136 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 10.02.20 19:17, David Hildenbrand wrote: > On 07.02.20 12:39, Christian Borntraeger wrote: >> From: Claudio Imbrenda >> >> With the introduction of protected KVM guests on s390 there is now a >> concept of inaccessible pages. These pages need to be made accessible >> before the host can access them. >> >> While cpu accesses will trigger a fault that can be resolved, I/O >> accesses will just fail. We need to add a callback into architecture >> code for places that will do I/O, namely when writeback is started or >> when a page reference is taken. >=20 > My question would be: What guarantees that the page will stay accessibl= e > (for I/O)? IIRC, pages can be converted back to secure/inaccessible > whenever the guest wants to access them. How will that be dealt with? Yes, in patch 5 we do use the page lock, PageWriteBack and page_ref_freez= e to only make the page secure again if no I/O is going to be started or still running. We have minimized the common code impact (just these 3 callbacks) so that= =20 architecture code can do the right thing. >=20 > I would assume some magic counter that tracks if the page still has to > remain accessible. Once all clients that require the page to be > "accessible" on the I/O path are done, the page can be made inaccessibl= e > again. But then, I would assume there would be something like a >=20 > /* make page accessible and make sure the page will remain accessible *= / > arch_get_page_accessible(page); >=20 > /* we're done dealing with the page content */ > arch_put_page_accessible(page); >=20 > You mention page references. I think you should elaborate how that is > expected to work in the patch description more detailed. >=20 >=20 > (side note: I assume you guys have a plan for dealing with kdump wantin= g > to dump inaccessible pages. the kexec kernel would have to talk to the > UV to convert pages - and also make pages accessible on the I/O path I > guess - or one would want to mark and skip encrypted pages completely i= n > kdump somehow, as the content is essentially garbage) On kexec and kdump the ultravisor is called as part of the the diagnose 308 subcodes 0 and 1 to make sure that a: kdump works (no fault on a=20 previously secure page) and b: the content of the secure page is no=20 longer accessible.