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Date:   Tue, 30 Jul 2019 17:01:19 +0200
From:   Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= 
        <marmarek@invisiblethingslab.com>
To:     Souptick Joarder <jrdr.linux@gmail.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>,
        Juergen Gross <jgross@suse.com>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        robin.murphy@arm.com, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
        stable@vger.kernel.org, Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [Xen-devel] [PATCH v4 8/9] xen/gntdev.c: Convert to use
 vm_map_pages()
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On Tue, Jul 30, 2019 at 08:22:02PM +0530, Souptick Joarder wrote:
> On Tue, Jul 30, 2019 at 7:52 PM Marek Marczykowski-G=C3=B3recki
> <marmarek@invisiblethingslab.com> wrote:
> >
> > On Tue, Jul 30, 2019 at 10:05:42AM -0400, Boris Ostrovsky wrote:
> > > On 7/30/19 2:03 AM, Souptick Joarder wrote:
> > > > On Mon, Jul 29, 2019 at 7:06 PM Marek Marczykowski-G=C3=B3recki
> > > > <marmarek@invisiblethingslab.com> wrote:
> > > >> On Mon, Jul 29, 2019 at 02:02:54PM +0530, Souptick Joarder wrote:
> > > >>> On Mon, Jul 29, 2019 at 1:35 PM Souptick Joarder <jrdr.linux@gmai=
l.com> wrote:
> > > >>>> On Sun, Jul 28, 2019 at 11:36 PM Marek Marczykowski-G=C3=B3recki
> > > >>>> <marmarek@invisiblethingslab.com> wrote:
> > > >>>>> On Fri, Feb 15, 2019 at 08:18:31AM +0530, Souptick Joarder wrot=
e:
> > > >>>>>> Convert to use vm_map_pages() to map range of kernel
> > > >>>>>> memory to user vma.
> > > >>>>>>
> > > >>>>>> map->count is passed to vm_map_pages() and internal API
> > > >>>>>> verify map->count against count ( count =3D vma_pages(vma))
> > > >>>>>> for page array boundary overrun condition.
> > > >>>>> This commit breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_=
pages
> > > >>>>> will:
> > > >>>>>  - use map->pages starting at vma->vm_pgoff instead of 0
> > > >>>> The actual code ignores vma->vm_pgoff > 0 scenario and mapped
> > > >>>> the entire map->pages[i]. Why the entire map->pages[i] needs to =
be mapped
> > > >>>> if vma->vm_pgoff > 0 (in original code) ?
> > > >> vma->vm_pgoff is used as index passed to gntdev_find_map_index. It=
's
> > > >> basically (ab)using this parameter for "which grant reference to m=
ap".
> > > >>
> > > >>>> are you referring to set vma->vm_pgoff =3D 0 irrespective of val=
ue passed
> > > >>>> from user space ? If yes, using vm_map_pages_zero() is an altern=
ate
> > > >>>> option.
> > > >> Yes, that should work.
> > > > I prefer to use vm_map_pages_zero() to resolve both the issues. Alt=
ernatively
> > > > the patch can be reverted as you suggested. Let me know you opinion=
 and wait
> > > > for feedback from others.
> > > >
> > > > Boris, would you like to give any feedback ?
> > >
> > > vm_map_pages_zero() looks good to me. Marek, does it work for you?
> >
> > Yes, replacing vm_map_pages() with vm_map_pages_zero() fixes the
> > problem for me.
>=20
> Marek, I can send a patch for the same if you are ok.
> We need to cc stable as this changes are available in 5.2.4.

Sounds good, thanks!

--=20
Best Regards,
Marek Marczykowski-G=C3=B3recki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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