Re: [Xen-devel] 2.6.27-rc1 >4096MB issue

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Jan Beulich wrote:
> > > > Jeremy Fitzhardinge <jeremy@xxxxxxxx> 05.08.08 05:07 >>>
> > > >         
> > Subject: make PFN_PHYS explicitly return 64-bit result
> >
> > PFN_PHYS, as its name suggests, turns a pfn into a physical address.
> > However, it is a macro which just operates on its argument without
> > modifying its type.  pfns are typed unsigned long, but an unsigned
> > long may not be long enough to hold a physical address (32-bit systems
> > with more than 32 bits of physcial address).  This means that the
> > resulting address could be truncated if it doesn't fit within an
> > unsigned long.  This isn't generally a problem because most users end
> > up using it for "low" memory, but there's no reason why PFN_PHYS
> > couldn't be used for any possible pfn.
> >
> > Unfortunately there's no univerally recognized type for holding a full
> > physical address, so this patch makes it always return a u64 result.
> >     
> Couldn't you use resource_size_t here?
Yeah, looks like I can.  It had crossed my mind, but I'd vaguely 
remembered that it might no be set if you don't have 64-bit IO devices.  
But it looks like it's set for all interesting cases (64 bit machines, 
and 32-bit x86 PAE).
   J

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