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Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
- To: Matthew Wilcox <willy@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>
- From: David Hildenbrand <david@xxxxxxxxxx>
- Date: Tue, 12 Mar 2019 18:23:43 +0100
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- Cc: Juergen Gross <jgross@xxxxxxxx>, k.khlebnikov@xxxxxxxxxxx, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "VMware, Inc." <pv-drivers@xxxxxxxxxx>, osstest service owner <osstest-admin@xxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, linux-mm@xxxxxxxxx, Julien Freche <jfreche@xxxxxxxxxx>, Nadav Amit <namit@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Delivery-date: Tue, 12 Mar 2019 17:23:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
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@xxxxxxxxxxxxx>
>>> 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:
Just to clarify on that point, XEN balloon does not use balloon
compaction as far as I know (only virtio-balloon and as far as I know
now also vmware balloon). Both of them don't map any such pages to user
space, so it never was and isn't a problem.
>
> commit d6d86c0a7f8ddc5b38cf089222cb1d9540762dc2
> Author: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>
> 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.
>
--
Thanks,
David / dhildenb
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