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Tue, 12 Mar 2019 18:02:44 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 12 Mar 2019 11:02:44 -0700 Subject: Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm) To: Andrew Cooper , David Hildenbrand , Matthew Wilcox , Julien Grall Cc: Juergen Gross , k.khlebnikov@samsung.com, Stefano Stabellini , Kees Cook , Konrad Rzeszutek Wilk , "VMware, Inc." , osstest service owner , "linux-kernel@vger.kernel.org" , linux-mm@kvack.org, Julien Freche , Nadav Amit , xen-devel@lists.xenproject.org References: <80211e70-5f54-9421-8e8f-2a4fc758ce39@arm.com> <46118631-61d4-adb6-6ffc-4e7c62ea3da9@arm.com> <20190312171421.GJ19508@bombadil.infradead.org> <45323ea0-2a50-8891-830e-e1f8a8ed23ea@citrix.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; prefer-encrypt=mutual; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <45323ea0-2a50-8891-830e-e1f8a8ed23ea@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9193 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903120122 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 3/12/19 1:24 PM, Andrew Cooper wrote: > On 12/03/2019 17:18, David Hildenbrand wrote: >> On 12.03.19 18:14, Matthew Wilcox wrote: >>> On Tue, Mar 12, 2019 at 05:05:39PM +0000, Julien Grall wrote: >>>> On 3/12/19 3:59 PM, Julien Grall wrote: >>>>> It looks like all the arm test for linus [1] and next [2] tree >>>>> are now failing. x86 seems to be mostly ok. >>>>> >>>>> The bisector fingered the following commit: >>>>> >>>>> commit 0ee930e6cafa048c1925893d0ca89918b2814f2c >>>>> Author: Matthew Wilcox >>>>> Date: Tue Mar 5 15:46:06 2019 -0800 >>>>> >>>>> mm/memory.c: prevent mapping typed pages to userspace >>>>> Pages which use page_type must never be mapped to userspace as it would >>>>> destroy their page type. Add an explicit check for this instead of >>>>> assuming that kernel drivers always get this right. >>> Oh good, it found a real problem. >>> >>>> It turns out the problem is because the balloon driver will call >>>> __SetPageOffline() on allocated page. Therefore the page has a type and >>>> vm_insert_pages will deny the insertion. >>>> >>>> My knowledge is quite limited in this area. So I am not sure how we can >>>> solve the problem. >>>> >>>> I would appreciate if someone could provide input of to fix the mapping. >>> I don't know the balloon driver, so I don't know why it was doing this, >>> but what it was doing was Wrong and has been since 2014 with: >>> >>> commit d6d86c0a7f8ddc5b38cf089222cb1d9540762dc2 >>> Author: Konstantin Khlebnikov >>> Date: Thu Oct 9 15:29:27 2014 -0700 >>> >>> mm/balloon_compaction: redesign ballooned pages management >>> >>> If ballooned pages are supposed to be mapped into userspace, you can't mark >>> them as ballooned pages using the mapcount field. >>> >> Asking myself why anybody would want to map balloon inflated pages into >> user space (this just sounds plain wrong but my understanding to what >> XEN balloon driver does might be limited), but I assume the easy fix >> would be to revert > I suspect the bug here is that the balloon driver is (ab)used for a > second purpose Yes. And its name is alloc_xenballooned_pages(). -boris > - to create a hole in pfn space to map some other bits of > shared memory into. > > I think at the end of the day, what is needed is a struct page_info > which looks like normal RAM, but the backing for which can be altered by > hypercall to map other things. > > ~Andrew