From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
David Hildenbrand <david@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Julien Grall <julien.grall@arm.com>
Cc: Juergen Gross <jgross@suse.com>,
k.khlebnikov@samsung.com,
Stefano Stabellini <sstabellini@kernel.org>,
Kees Cook <keescook@chromium.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
"VMware, Inc." <pv-drivers@vmware.com>,
osstest service owner <osstest-admin@xenproject.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Julien Freche <jfreche@vmware.com>,
Nadav Amit <namit@vmware.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
Date: Tue, 12 Mar 2019 14:02:31 -0400 [thread overview]
Message-ID: <f4b40d91-9c41-60ed-6b4e-df47af8e5292@oracle.com> (raw)
In-Reply-To: <45323ea0-2a50-8891-830e-e1f8a8ed23ea@citrix.com>
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 <willy@infradead.org>
>>>>> 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 <k.khlebnikov@samsung.com>
>>> 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
next prev parent reply other threads:[~2019-03-12 18:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <E1h3Uiq-0002L6-Ij@osstest.test-lab.xenproject.org>
[not found] ` <80211e70-5f54-9421-8e8f-2a4fc758ce39@arm.com>
2019-03-12 17:05 ` xen: Can't insert balloon page into VM userspace (WAS Re: [Xen-devel] [linux-linus bisection] complete test-arm64-arm64-xl-xsm) Julien Grall
2019-03-12 17:14 ` Matthew Wilcox
2019-03-12 17:18 ` David Hildenbrand
2019-03-12 17:24 ` [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS " Andrew Cooper
2019-03-12 18:02 ` Boris Ostrovsky [this message]
2019-03-12 18:11 ` Andrew Cooper
2019-03-12 18:23 ` David Hildenbrand
2019-03-12 19:46 ` David Hildenbrand
2019-03-14 8:37 ` Juergen Gross
2019-03-14 14:12 ` Julien Grall
2019-03-14 14:14 ` David Hildenbrand
2019-03-14 14:15 ` Juergen Gross
2019-03-14 14:16 ` David Hildenbrand
2019-03-12 17:39 ` xen: Can't insert balloon page into VM userspace (WAS Re: [Xen-devel] " Julien Grall
2019-03-12 17:49 ` David Hildenbrand
2019-03-12 17:23 ` David Hildenbrand
2019-03-12 17:25 ` Nadav Amit
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