linux-kernel - Re: x86: potential ioremap() issues

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Date:	Thu, 28 Feb 2008 14:30:07 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: x86: potential ioremap() issues

>> - When ioremap_page_range() fails, remove_vm_area() is used rather
>>   than vunmap() - I think this will cause a 'struct vm_struct' leak.
>
>indeed, good catch - could you check whether the patch below fixes this? 

Yes, it certainly does. You using it rather than vunmap() makes me notice
other inconsistencies (but harmless in nature): The ioremap_change_attr()
failure case should use the same function, and iounmap() could be
simplified using it, too.

Acked-by: Jan Beulich <jbeulich@...ell.com>

>> - While ioremap() continues to happily map RAM pages (with a bogus
>>   [see below] WARN_ON_ONCE()), cacheability of the memory is not
>>   being restored in iounmap().
>
>correct - these are never supposed to be 'true', generally allocated RAM 
>pages - or like we do with AGP where the pages are exclusively owned we 
>restore their cacheability explicitly.

Never supposed to be doesn't mean they really aren't. I think as long as
one permits it, the other should undo its effects. Further more, it would
seem to me that you could easily ioremap() a hot-pluggable (but
unpopulated) memory range, and get into inconsistencies once that
range gets actually populated. Or am I not seeing a safeguard
preventing this?

>> - The check for RAM pages (except for the WARN_ON_ONCE())
>>   continues to be applied only to lowmem pages.
>
>yes, the biggest constraint from ioremap comes when it applies to pages 
>that are mapped by the kernel. But i guess we could extend this to all 
>things RAM ... the second patch below does this. What do you think? I've 
>queued this up in x86.git#testing as well.

Yes, that's exactly what I would have thought it should look like.

Acked-by: Jan Beulich <jbeulich@...ell.com>

>> - The WARN_ON_ONCE() itself is applied to the pfn after the
>>   preceding loop finished, i.e. to a pfn that doesn't actually participate
>>   in the operation. Shouldn't it be moved inside the loop?
>
>i removed the WARN_ON_ONCE() from x86.git a few days ago, it's lined up 
>for the next push.

Great, thanks!

Jan

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