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Date:   Tue, 27 Aug 2019 12:49:35 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Souptick Joarder <jrdr.linux@gmail.com>
Cc:     leon@kernel.org, Doug Ledford <dledford@redhat.com>,
        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] IB/mlx5: Convert to use vm_map_pages_zero()
Message-ID: <20190827154935.GD7149@ziepe.ca>
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On Tue, Aug 27, 2019 at 01:48:57AM +0530, Souptick Joarder wrote:
> On Mon, Aug 26, 2019 at 5:50 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Mon, Aug 26, 2019 at 01:32:09AM +0530, Souptick Joarder wrote:
> > > On Mon, Aug 26, 2019 at 1:13 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > > >
> > > > On Sun, Aug 25, 2019 at 11:37:27AM +0530, Souptick Joarder wrote:
> > > > > First, length passed to mmap is checked explicitly against
> > > > > PAGE_SIZE.
> > > > >
> > > > > Second, if vma->vm_pgoff is passed as non zero, it would return
> > > > > error. It appears like driver is expecting vma->vm_pgoff to
> > > > > be passed as 0 always.
> > > >
> > > > ? pg_off is not zero
> > >
> > > Sorry, I mean, driver has a check against non zero to return error -EOPNOTSUPP
> > > which means in true scenario driver is expecting vma->vm_pgoff should be passed
> > > as 0.
> >
> > get_index is masking vm_pgoff, it is not 0
> 
> Sorry, I missed this part. Further looking into code,
> in mlx5_ib_mmap(), vma_vm_pgoff is used to get command and
> inside mlx5_ib_mmap_clock_info_page() entire *dev->mdev->clock_info*
> is mapped.
> 
> Consider that, the below modification will only take care of vma length
> error check inside vm_map_pages_zero() and an extra check for vma
> length is not needed.

What is the point of vm_map_pages_zero() Is there some reason we should
prefer it for mapping a single page?

Jason