linux-kernel - Re: Replacement for page fault notifiers?

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Date:	Wed, 09 Jan 2008 20:30:04 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Pavel Roskin <proski@....org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Airlie <airlied@...il.com>, Pekka Paalanen <pq@....fi>,
	linux-kernel@...r.kernel.org, jbeulich@...ell.com
Subject: Re: Replacement for page fault notifiers?


On Wed, 2008-01-09 at 21:21 -0500, Pavel Roskin wrote:
> On Wed, 2008-01-09 at 20:03 -0600, Matt Mackall wrote:
> 
> > That makes it way too easy for drivers of questionable legality to just
> > clear that bit. Also, we've got a shortage of page bits, etc.
> 
> If we ever have this problem, the bit can be changed in the kernel to
> fool those drivers (I hope the shortage is not so dire that there will
> be no more bits left).

That's what we call an arms race. And yes, page bits are close to
running out on 32-bit.

> I don't think evil drivers should be a problem per se.  There are
> existing non-free drivers that still need to be traced over and over
> again.  I guess ndiswrapper could use tracing for Windows drivers that
> don't know anything about Linux page flags.
> 
> Last but not least, mmiotrace should be useful for free drivers in the
> first place to have a legitimate reason to be in the kernel.

I definitely agree that tracing MMIO is an extremely useful feature.
I've implemented it myself once already for 2.4.

-- 
Mathematics is the supreme nostalgia of our time.

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