linux-kernel - Re: get_user_pages() cache issues on ARM

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Message-ID: <20060930170548.GA24949@flint.arm.linux.org.uk>
Date:	Sat, 30 Sep 2006 18:05:48 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	dhylands@...il.com, guinan@...ebutton.com,
	linux-kernel@...r.kernel.org
Subject: Re: get_user_pages() cache issues on ARM

On Sat, Sep 30, 2006 at 06:59:50PM +0200, Miklos Szeredi wrote:
> Hi Russell,
> 
> The get_user_pages() vs dcache coherency issue still seems to be
> unresolved on ARM.
> 
> See flush_anon_page() and flush_kernel_dcache_page() in
> Documentation/cachetlb.txt and their implementation on PARISC.
> 
> Can you please take a look at this?

I'm sorry, I don't think I have sufficient understanding of the Linux VM
to look at these issues anymore.

The questions I have are:

- where do these pages that get_user_pages() finds and calls flush_anon_page()
  on come from?
- why is the current ARM flush_dcache_page() (which is also called after
  flush_anon_page()) not sufficient?
- if we implement flush_anon_page() does that mean that we end up flushing
  multiple times in some circumstances?  If so, how do we avoid this?

I'm really serious - I no longer understand the Linux VM sufficiently to
get this stuff right.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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