linux-kernel - Re: m(un)map kmalloc buffers to userspace

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Message-ID: <20151209135544.GE30907@dhcp22.suse.cz>
Date:	Wed, 9 Dec 2015 14:55:44 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Sebastian Frias <sebastian_frias@...madesigns.com>
Cc:	linux-mm@...ck.org, Marc Gonzalez <marc_gonzalez@...madesigns.com>,
	linux-kernel@...r.kernel.org
Subject: Re: m(un)map kmalloc buffers to userspace

On Tue 08-12-15 18:25:31, Sebastian Frias wrote:
> Hi,
> 
> We are porting a driver from Linux 3.4.39+ to 4.1.13+, CPU is Cortex-A9.
> 
> The driver maps kmalloc'ed memory to user space.

This sounds like a terrible idea to me. Why don't you simply use the
page allocator directly? Try to imagine what would happen if you mmaped
a kmalloc with a size which is not page aligned? mmaped memory uses
whole page granularity.
-- 
Michal Hocko
SUSE Labs
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