Date: Wed, 9 Dec 2015 16:12:55 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Sebastian Frias <sebastian_frias@sigmadesigns.com>
Cc: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
        linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: m(un)map kmalloc buffers to userspace
Message-ID: <20151209151254.GH30907@dhcp22.suse.cz>
References: <5667128B.3080704@sigmadesigns.com>
 <20151209135544.GE30907@dhcp22.suse.cz>
 <566835B6.9010605@sigmadesigns.com>
 <20151209143207.GF30907@dhcp22.suse.cz>
 <56684062.9090505@sigmadesigns.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <56684062.9090505@sigmadesigns.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1470
Lines: 34

On Wed 09-12-15 15:53:22, Sebastian Frias wrote:
[...]
> 2) Now that VM_RESERVED was removed, is there another recommended flag to
> replace it for the purposes above?

VM_IO + potentially others depending on your usecase.

> 3) Since it was working before, we suppose that something that was
> previously done by default on the kernel it is not done anymore, could that
> be a remap_pfn_range during mmap or kmalloc?

VM_RESERVED removal was a cleanup which has removed the flag because it
was not needed and the same effect could be implied from either VM_IO or 
VM_DONTEXPAND | VM_DONTDUMP. See 314e51b9851b ("mm: kill vma flag
VM_RESERVED and mm->reserved_vm counter") for more detailed information.

> 4) We tried using remap_pfn_range inside mmap and while it seems to work, we
> still get occasional crashes due to corrupted memory (in this case the
> behaviour is the same between 4.1 and 3.4 when using the same modified
> driver), are we missing something?

This is hard to tell without knowing your driver. I would just encourage
you to look at other drivers which map kernel memory to userspace via
mmap. There are many of them. Maybe you can find a pattern which suites
your usecase.

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/