Messages in this thread | | | Date | Tue, 12 Mar 2019 10:14:21 -0700 | From | Matthew Wilcox <> | Subject | Re: xen: Can't insert balloon page into VM userspace (WAS Re: [Xen-devel] [linux-linus bisection] complete test-arm64-arm64-xl-xsm) |
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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.
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