linux-kernel - Re: [PATCH v2] xen/balloon: Fix mapping PG

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Message-ID: <d02a354b-6b40-6fd9-b09b-debfee7d2071@suse.com>
Date:   Thu, 14 Mar 2019 17:05:33 +0100
From:   Juergen Gross <jgross@...e.com>
To:     David Hildenbrand <david@...hat.com>,
        xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Julien Grall <julien.grall@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Nadav Amit <namit@...are.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>,
        Jan Beulich <JBeulich@...e.com>
Subject: Re: [PATCH v2] xen/balloon: Fix mapping PG_offline pages to user
 space

On 14/03/2019 17:02, David Hildenbrand wrote:
> The XEN balloon driver - in contrast to other balloon drivers - allows
> to map some inflated pages to user space. Such pages are allocated via
> alloc_xenballooned_pages() and freed via free_xenballooned_pages().
> The pfn space of these allocated pages is used to map other things
> by the hypervisor using hypercalls.
> 
> Pages marked with PG_offline must never be mapped to user space (as
> this page type uses the mapcount field of struct pages).
> 
> So what we can do is, clear/set PG_offline when allocating/freeing an
> inflated pages. This way, most inflated pages can be excluded by
> dumping tools and the "reused for other purpose" balloon pages are
> correctly not marked as PG_offline.
> 
> Fixes: 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
> Reported-by: Julien Grall <julien.grall@....com>
> Tested-by: Julien Grall <julien.grall@....com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen