linux-kernel - Re: [PATCH v2] staging: zsmalloc: Ensure handle is never 0 on success

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Date:	Tue, 12 Nov 2013 09:06:37 -0800
From:	Olav Haugan <ohaugan@...eaurora.org>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	ngupta@...are.org, sjenning@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, minchan@...nel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2] staging: zsmalloc: Ensure handle is never 0 on success

Hi Greg,

On 11/11/2013 4:19 PM, Greg KH wrote:
> On Thu, Nov 07, 2013 at 05:58:03PM -0800, Olav Haugan wrote:
>> zsmalloc encodes a handle using the pfn and an object
>> index. On hardware platforms with physical memory starting
>> at 0x0 the pfn can be 0. This causes the encoded handle to be
>> 0 and is incorrectly interpreted as an allocation failure.
> 
> Please list the known hardware platforms that have this issue, so that
> people have a chance to know if this patch is relevant for them or not.
> 
> For example, should I include this in the stable releases because it
> affects systems that are shipping?  Or is it just in "future" chips and
> it doesn't need to go there or not?
> 
> Please make it easy for me to do this type of determination, I already
> asked you this question before, why didn't you include the information
> here as well (hint, that is why I asked you...)

I don't think it would be the best to mention specific hardware
platforms in the commit text. If I saw this patch listing specific
hardware platforms I would have made the wrong decision (I would look at
the list and decide that I am not running on those platforms so I don't
need this patch). The problem could happen on any hardware platform. It
just depends on how the memory map of the platform is configured. Hence,
I re-worded the commit text to make it clear that this will happen when
you have memory starting at 0x0.

If I list out specific hardware platforms it would be only a sample (I
do not know all hardware platforms and their memory maps). However,
having said that there are products already shipping with physical
address starting at 0.

Thanks,

Olav Haugan

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