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

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Message-Id: <E1GTiTy-0002kU-00@dorka.pomaz.szeredi.hu>
Date:	Sat, 30 Sep 2006 19:18:34 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	rmk+lkml@....linux.org.uk
CC:	James.Bottomley@...eleye.com, dhylands@...il.com,
	guinan@...ebutton.com, linux-kernel@...r.kernel.org
Subject: Re: get_user_pages() cache issues on ARM

Added James Bottomley to the CC.  He designed this interface, and he
explained to me how it's supposed to work, but I since forgot.

James, do you have some memory of these issues?

Thanks,
Miklos

> > 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.
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