linux-kernel - Re: User switchable HW mappings & cie

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Date:	Mon, 9 Oct 2006 20:36:47 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Thomas Hellström 
	<thomas@...gstengraphics.com>, linux-mm@...ck.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>, Arnd Bergmann <arnd@...db.de>,
	Linus Torvalds <torvalds@...l.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: User switchable HW mappings & cie

Hi all,

On Monday, 9. October 2006 13:51, Benjamin Herrenschmidt wrote:
> > One problem that occurs is that the rule for ptes with non-backing 
> > struct pages
> > Which I think was introduced in 2.6.16:
> > 
> >     pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
> > 
> > cannot be honored, at least not with the DRM memory manager, since the 
> > graphics object will be associated with a vma and not the underlying 
> > physical address. User space will have vma->vm_pgoff as a handle to the 
> > object, which may move around in graphics memory.
> 
> That's a problem with VM_PFNMAP set indeed. get_user_pages() is a
> non-issue with VM_IO set too but I'm not sure about other code path that
> might try to hit here... though I think we don't hit that if MAP_SHARED,
> Nick ?

Istn't this just a non-linear PFN mapping, you are describing here?

Nick: 
	Cant your new fault consolidation code handle that?
	AFAICS your new .fault handler just gets the
	vma and pgoff and install the matching PTE via install_THINGIE()
	or vm_insert_THINGIE()

Or do I miss sth. here?


Regards

Ingo Oeser
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