Re: [PATCH 1/2] x86: ioremap: fix wrong physical address handling

H. Peter Anvin
2010-06-17T13:47:01Z

On 06/17/2010 02:35 AM, Jeremy Fitzhardinge wrote:
>>>
>>> By the way, is there linux kernel limit regarding above 44-bits physical
>>> address in x86_32 PAE? For example, pfn above 32-bits is not supported?
>
> That's an awkward situation. I would tend to suggest that you not
> support this type of machine with a 32-bit kernel. Is it a sparse
> memory system, or is there a device mapped in that range?
>
> I guess it would be possible to special-case ioremap to allow the
> creation of such mappings, but I don't know what kind of system-wide
> fallout would happen as a result. The consequences of something trying
> to extract a pfn from one of those ptes would be
>
>> There are probably places at which PFNs are held in 32-bit numbers,
>> although it would be good to track them down if it isn't too expensive
>> to fix them (i.e. doesn't affect generic code.)
>>
>
> There are many places which hold pfns in 32 bit variables on 32 bit
> systems; the standard type for pfns is "unsigned long", pretty much
> everywhere in the kernel. It might be worth defining a pfn_t and
> converting usage over to that, but it would be a pervasive change.
>

I think you're right, and just making 2^44 work correctly would be good
enough. Doing special forwarding of all 52 bits of the real physical
address in the paravirt case (where it is self-contained and doesn't
spill into the rest of the kernel) would probably be a good thing, though.

-hpa

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