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[209.132.183.28]) by mx.google.com with ESMTPS id n32si3101753qvc.145.2019.03.12.12.46.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 12:46:25 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7611B30833C0; Tue, 12 Mar 2019 19:46:24 +0000 (UTC) Received: from [10.36.116.121] (ovpn-116-121.ams2.redhat.com [10.36.116.121]) by smtp.corp.redhat.com (Postfix) with ESMTP id 17BB21001E70; Tue, 12 Mar 2019 19:46:20 +0000 (UTC) Subject: Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm) From: David Hildenbrand To: Boris Ostrovsky , Andrew Cooper , 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> <9a40e1ff-7605-e822-a1d2-502a12d0fba7@redhat.com> Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <9a40e1ff-7605-e822-a1d2-502a12d0fba7@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Tue, 12 Mar 2019 19:46:24 +0000 (UTC) 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 12.03.19 19:23, David Hildenbrand wrote: > On 12.03.19 19:02, Boris Ostrovsky wrote: >> 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(). >> > > Haven't had a look at the code yet, but would another temporary fix be > to clear/set PG_offline when allocating/freeing a ballooned page? > (assuming here that only such pages will be mapped to user space) > I guess something like this could do the trick if I understood it correctly: diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 39b229f9e256..d37dd5bb7a8f 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages) while (pgno < nr_pages) { page = balloon_retrieve(true); if (page) { + __ClearPageOffline(page); pages[pgno++] = page; #ifdef CONFIG_XEN_HAVE_PVMMU /* @@ -645,8 +646,10 @@ void free_xenballooned_pages(int nr_pages, struct page **pages) mutex_lock(&balloon_mutex); for (i = 0; i < nr_pages; i++) { - if (pages[i]) + if (pages[i]) { + __SetPageOffline(pages[i]); balloon_append(pages[i]); + } } balloon_stats.target_unpopulated -= nr_pages; At least this way, the pages allocated (and thus eventually mapped to user space) would not be marked, but the other ones would remain marked and could be excluded by makedumptool. -- Thanks, David / dhildenb