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From:   Nadav Amit <namit@vmware.com>
To:     Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Oleksandr Natalenko <onatalen@redhat.com>
CC:     Xavier Deguillard <xdeguillard@vmware.com>,
        pv-drivers <pv-drivers@vmware.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Gil Kupfer <gilkup@gmail.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v2] vmw_balloon: fixing double free when batching mode is
 off
Thread-Topic: [PATCH v2] vmw_balloon: fixing double free when batching mode is
 off
Thread-Index: AQHTujhdSIiXJAlj90GNO4oOVtEcZaPPHhoAgAjUbYA=
Date:   Mon, 19 Mar 2018 18:52:53 +0000
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 <20180312192848.22104-1-namit@vmware.com>
 <E63288C3-BE4F-4D41-A074-1CB86C74414E@vmware.com>
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Nadav Amit <namit@vmware.com> wrote:

> Nadav Amit <namit@vmware.com> wrote:
>=20
>> From: Gil Kupfer <gilkup@gmail.com>
>>=20
>> The balloon.page field is used for two different purposes if batching is
>> on or off. If batching is on, the field point to the page which is used
>> to communicate with with the hypervisor. If it is off, balloon.page
>> points to the page that is about to be (un)locked.
>>=20
>> Unfortunately, this dual-purpose of the field introduced a bug: when the
>> balloon is popped (e.g., when the machine is reset or the balloon driver
>> is explicitly removed), the balloon driver frees, unconditionally, the
>> page that is held in balloon.page.  As a result, if batching is
>> disabled, this leads to double freeing the last page that is sent to the
>> hypervisor.
>=20
> Oleksandr, if you can confirm that it fixes the bug you encountered, it
> would be great.
>=20
> Greg, Arnd, on your free time, please let me know if there is any issue
> with the patch, and whether you can incorporate it, preferably in 4.16,
> since it is a bug-fix that was encountered by Red-Hat customers.

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