linux-kernel - Re: [rfc][patch] remove nopage

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Date:	Wed, 14 Nov 2007 14:26:35 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ia64@...r.kernel.org, rth@...ddle.net,
	Jaya Kumar <jayakumar.lkml@...il.com>, krh@...hat.com,
	stefanr@...6.in-berlin.de, rolandd@...co.com,
	mshefty@...ips.intel.com, hal.rosenstock@...il.com,
	avi@...ranet.com, mchehab@...radead.org, dgilbert@...erlog.com,
	Greg Kroah-Hartman <greg@...ah.com>, jgarzik@...ox.com,
	perex@...ex.cz, Karsten Wiese <annabellesgarden@...oo.de>
Subject: Re: [rfc][patch] remove nopage

At Mon, 12 Nov 2007 02:56:43 +0100,
Nick Piggin wrote:
> 
> Hi all,
> 
> This is a patch to remove 'nopage' from the tree.
> 
> I've gone through all the drivers and converted them to use fault as best
> I can. When using fault, I've also tried to use vmf->pgoff rather than the
> virtual address to find the page (which is much preferred). Mostly it has
> been OK, but DRM is a bit difficult, as it seems to use vma->vm_pgoff as
> a 2nd dimension of addressing.
> 
> I've also done some other things while going through at the code...
> 
> Converted incorrect OOM returns to SIGBUS.  OOM should only be returned as a
> result of a memory allocation failure. We will actually want the fault path OOM
> handling to be unified with the normal OOM killing path in future, and that
> means the box will panic if panic_on_oom is set, or it will oom-kill random
> processes before retrying the fault, etc.  SIGBUS means something like
> "physical address (ie. after translation) does not exist", which is appropriate
> AFAIKS in all cases (but please double check).
> 
> Got rid of some bogus looking "disallow mremap" checks that just check for
> address > vma->vm_end. Am I missing something here? Presumably this is supposed
> to prevent an mremap expanding the mapping outside the limit of the underlying
> resource, but actually mremap will update vma->vm_end, and anyway this
> condition is already checked in the page fault code. Others seem to get this
> right by checking the underlying resource itself. Others don't seem to even
> care. Might be a fair window for corruption / security problems here. Probably
> we need a flag that explicitly prevents mremap() so driver writers don't have
> to think too hard.
> 
> Now all these are going to need to be split up properly, but if we can
> take a look at this all together, the discussion will be more coherent ;)

The changes in the sound stuff look OK.  It works fine as long as I've
tested.


thanks,

Takashi
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