linux-kernel - Re: [PATCH 2/2] make /dev/kmem return error for highmem

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Message-ID: <51156494.3050300@zytor.com>
Date:	Fri, 08 Feb 2013 12:48:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, bp@...en8.de,
	mingo@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH 2/2] make /dev/kmem return error for highmem

On 02/08/2013 12:28 PM, Dave Hansen wrote:
> I was auding the /dev/mem code for more questionable uses of
> __pa(), and ran across this.
>
> My assumption is that if you use /dev/kmem, you expect to be
> able to read the kernel virtual mappings.  However, those
> mappings _stop_ as soon as we hit high memory.  The
> pfn_valid() check in here is good for memory holes, but since
> highmem pages are still valid, it does no good for those.
>
> Also, since we are now checking that __pa() is being done on
> valid virtual addresses, this might have tripped the new
> check.  Even with the new check, this code would have been
> broken with the NUMA remapping code had we not ripped it
> out:
>

It would be great if you could take a stab at fixing /dev/mem and 
/dev/kmem... there are a bunch of problems with both which seem to 
really translate to "HIGHMEM was never properly implemented"...

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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