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Message-ID: <20100117094043.0483ee1a@infradead.org> Date: Sun, 17 Jan 2010 09:40:43 -0800 From: Arjan van de Ven <arjan@...radead.org> To: Felix Rubinstein <felixru@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: /dev/mem implementation On Sun, 17 Jan 2010 18:47:10 +0200 Felix Rubinstein <felixru@...il.com> wrote: > I see the motivation to limit the access to DRAM from root account > CONFIG_STRICT_DEVMEM by mmap'ing /dev/[k]mem but it's easily overruled > by simple char driver and implementing mmap of it's own totally > bypassing all limitations. > > What do you think about it guy? > Appreciate it. the reason PAT bans parts of /dev/mem is simple: it is illegal to have mapping aliases (different cachability) for the same physical page. Normal kernel APIs take care of this for the normal case, but /dev/mem would be a back door into that. This is a hardware imposed requirement, and violating the rule can have really nasty consequences... hence the PAT code just not allowing it. If you feel that you have a valid use case where you really want do muck with such memory, it might be a good idea to explain that usecase.... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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