On 05/27/2014 07:10 AM, Matt Fleming wrote: > We need to check that a pfn is valid before handing it to pfn_to_page() > since on low memory systems with CONFIG_HIGHMEM=n it's possible that a > pfn may not have a corresponding struct page. > > This is in fact the case for one of Alan's machines where some of the > EFI boot services pages live in highmem, and running a kernel without > CONFIG_HIGHMEM enabled results in the following oops ... > diff --git a/mm/bootmem.c b/mm/bootmem.c > index 90bd3507b413..406e9cb1d58c 100644 > --- a/mm/bootmem.c > +++ b/mm/bootmem.c > @@ -164,6 +164,9 @@ void __init free_bootmem_late(unsigned long physaddr, > unsigned long size) > end = PFN_DOWN(physaddr + size); > > for (; cursor < end; cursor++) { > + if (!pfn_valid(cursor)) > + continue; > + > __free_pages_bootmem(pfn_to_page(cursor), 0); > totalram_pages++; > }
I don't think this is quite right. pfn_valid() tells us whether we have a 'struct page' there or not. *BUT*, it does not tell us whether it is RAM that we can actually address and than can be freed in to the buddy allocator. I think sparsemem is where this matters. Let's say mem= caused lowmem to end in the middle of a section (or that 896MB wasn't section-aligned). Then someone calls free_bootmem_late() on an area that is in the last section, but _above_ max_mapnr. It'll be pfn_valid(), we'll free it in to the buddy allocator, and we'll blam the first time we try to write to a bogus vaddr after a phys_to_virt(). At a higher level, I don't like the idea of the bootmem code papering over bugs when somebody calls in to it trying to _free_ stuff that's not memory (as far as the kernel is concerned). I think the right thing to do is to call in to the e820 code and see if the range is E820_RAM before trying to bootmem-free it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/