linux-kernel - Re: [Xen-devel] [PATCH v4 8/9] xen/gntdev.c: Convert to use vm_map

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Message-ID: <CAFqt6zZOymx8RH75F69exukLYcGd45xpUHkRHK8nYXpwF8co6g@mail.gmail.com>
Date:   Tue, 30 Jul 2019 20:22:02 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Juergen Gross <jgross@...e.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin.murphy@....com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        stable@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [Xen-devel] [PATCH v4 8/9] xen/gntdev.c: Convert to use vm_map_pages()

On Tue, Jul 30, 2019 at 7:52 PM Marek Marczykowski-Górecki
<marmarek@...isiblethingslab.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-Górecki
> > > <marmarek@...isiblethingslab.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@...il.com> wrote:
> > >>>> On Sun, Jul 28, 2019 at 11:36 PM Marek Marczykowski-Górecki
> > >>>> <marmarek@...isiblethingslab.com> wrote:
> > >>>>> On Fri, Feb 15, 2019 at 08:18:31AM +0530, Souptick Joarder wrote:
> > >>>>>> 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 = 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 map".
> > >>
> > >>>> are you referring to set vma->vm_pgoff = 0 irrespective of value passed
> > >>>> from user space ? If yes, using vm_map_pages_zero() is an alternate
> > >>>> option.
> > >> Yes, that should work.
> > > I prefer to use vm_map_pages_zero() to resolve both the issues. Alternatively
> > > 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.

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.

>
> --
> Best Regards,
> Marek Marczykowski-Górecki
> 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?