Re: xen: Can't insert balloon page into VM userspace (WAS Re: [Xen-devel] [linux...

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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From: Matthew Wilcox <[email protected]>
To: Julien Grall <[email protected]>
Cc: osstest service owner <[email protected]>,
	[email protected], Juergen Gross <[email protected]>,
	Konrad Rzeszutek Wilk <[email protected]>,
	Boris Ostrovsky <[email protected]>,
	Stefano Stabellini <[email protected]>,
	"[email protected]" <[email protected]>,
	Kees Cook <[email protected]>,
	[email protected], [email protected],
	Julien Freche <[email protected]>, Nadav Amit <[email protected]>,
	"VMware, Inc." <[email protected]>,
	[email protected]
Subject: Re: xen: Can't insert balloon page into VM userspace (WAS Re: [Xen-devel] [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
Date: Tue, 12 Mar 2019 10:14:21 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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 <[email protected]>
> > 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 <[email protected]>
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.

---

next      parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
     [not found] ` <[email protected]>
     [not found]   ` <[email protected]>
2019-03-12 17:14     ` Matthew Wilcox [this message]
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
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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