On Mon, Jul 12, 2010 at 09:28:16PM +0900, Minchan Kim wrote:
> It just checks that there is a section and section_mem_map has SECTION_HAS_MEM_MAP.
> The first section in above case has just 80M memory but section has 256M.
> So, 0x25000000 - 28000000 is the hole. If you pass pfn whihc is 0x2500000,
> let's see pfn_valid.
That's not a hole as such. It's an incompletely filled section, which is
precisely what sparsemem is all about.
> 1. We pass pfn_to_section_nr check
> 2. Both __nr_to_section and valid_section is vaild.
>
> static inline int pfn_valid(unsigned long pfn)
> {
> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> return 0;
> return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
> }
>
>
> What prevent above hole's case?
That looks too loose to be useful - that means invalid page table entries
can pass the pfn_valid() test when they should actually fail, and I'd
imagine there will be many more such problems like that.
> I think at least pfn_valid in sparsemem need bank range check like pfn_valid of ARM
> in FLATMEM.
I agree - pfn_valid() on sparsemem needs to be tightened.
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