Re: memblock and bootmem problems if start + size = 4GB

[Michal Simek]

Michal Simek wrote:
> Hi Tejun,
>
> > On Mon, Dec 19, 2011 at 02:58:13PM +0100, Michal Simek wrote:
> > > I have reached some problems with memblock and bootmem code for some 
> > > configurations.
> > > We can completely setup the whole system and all addresses in it.
> > > The problem happens if we place main memory to the end of address 
> > > space when
> > > mem_start + size reach 4GB limit.
> > >
> > > For example:
> > > mem_start      0xF000 0000
> > > mem_size       0x1000 0000 (or better lowmem size)
> > > mem_end        0xFFFF FFFF
> > > start + size 0x1 0000 0000 (u32 limit reached).
> > >
> > > I have done some patches which completely remove start + size values 
> > > from architecture specific
> > > code but I have found some problem in generic code too.
> > >
> > > For example in bootmem code where are three places where physaddr + 
> > > size is used.
> > > I would prefer to retype it to u64 because baseaddr and size don't 
> > > need to be 2^n.
> > >
> > > Is it correct solution? If yes, I will create proper patch.
> >
> > Yeah, that's an inherent problem in using [) ranges but I think
> > chopping off the last page probably is simpler and more robust
> > solution.  Currently, memblock_add_region() would simply ignore if
> > address range overflows but making it just ignore the last page is
> > several lines of addition.  Wouldn't that be effective enough while
> > staying very simple?
>
> The main problem is with PFN_DOWN/UP macros and it is in __init section.
> The result will be definitely u32 type (for 32bit archs) anyway and 
> seems to me
> better solution than ignoring the last page.
>
> Is there any internal kernel test code to test all pages - try to 
> allocate/use/test it?
> It will be especially good to do so on the last page to see if there is 
> any problem or not.
>
> That two conditions in memblock should be ok.

Tejun and Andrew: any other comment?

Thanks,
Michal

--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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